The Fund

The Offering

We may offer, from time to time, in one or more offerings, our common and/or fixed rate preferred shares, $0.001 par value per share, our notes, or our subscription rights to purchase our common or fixed rate preferred shares or both, which we refer to collectively as the “securities.” The Fund will not issue auction rate preferred shares in a public offering pursuant to this Prospectus. The securities may be

offered at prices and on terms to be set forth in one or more supplements to this Prospectus (each a “Prospectus Supplement”). The offering price per common share of the Fund will not be less than the net asset value per common share at the time we make the offering, exclusive of any underwriting commissions or discounts; however, transferable rights offerings that meet certain conditions may be offered at a price below the then current net asset value per common share of the Fund. You should read this Prospectus and the applicable Prospectus Supplement carefully before you invest in our securities. Our securities may be offered directly to one or more purchasers, through agents designated from time to time by us, or through underwriters or dealers. The Prospectus Supplement relating to the offering will identify any agents, underwriters or dealers involved in the sale of our shares, and will set forth any applicable purchase price, fee, commission or discount arrangement between us and our agents or underwriters, or among our underwriters, or the basis upon which such amount may be calculated. The Prospectus Supplement relating to any sale of fixed rate preferred shares will set forth the liquidation preference and information about the dividend period, dividend rate, any call protection or non-call period and other matters. The Prospectus Supplement relating to any sale of notes will set forth the principal amount, interest rate, interest payment dates, prepayment protection (if any), and other matters. The Prospectus Supplement relating to any offering of subscription rights will set forth the number of common and/or fixed rate preferred shares issuable upon the exercise of each right and the other terms of such rights offering.

Investment Objective and Policies

The Fund’s investment objective is to provide a high level of total return on its assets with an emphasis on dividends and income. The Fund will attempt to achieve its investment objective by investing, under normal market conditions, at least 80% of its net assets in dividend paying securities (such as common and preferred stock) or other income producing securities (such as fixed-income securities and securities that are convertible into common stock). In addition, under normal market conditions, at least 50% of the Fund’s total assets will consist of dividend paying equity securities. The Fund may invest in the securities of companies of any market capitalization. The Fund may invest up to 25% of its total assets in securities of issuers in a single industry and may invest up to 35% of its total assets in

securities of non-U.S. issuers (including securities of companies in emerging markets), which are generally denominated in foreign currencies. The Fund may also invest up to 10% of its total assets in below investment-grade securities, also known as high-yield securities. These securities, which may be preferred stock or debt, are predominantly speculative and involve major risk exposure to adverse conditions. Securities that are rated lower than “BBB” by Standard & Poor’s Rating Services (“S&P”) or lower than “Baa” by Moody’s Investors Service, Inc. (“Moody’s”) (or unrated debt securities of comparable quality) are referred to in the financial press as “junk bonds” or “high-yield” securities. The average duration of the Fund’s investments in debt securities is expected to vary and the Fund does not target any particular average duration. The Fund’s policy to invest at least 80% of its net assets in dividend paying securities or other income producing securities may be changed by the Board; however, if this policy changes, the Fund will provide shareholders at least 60 days’ written notice before implementation of the change in compliance with U.S. Securities and Exchange Commission (the “Commission” or the “SEC”) rules.

Preferred Shares

The terms of each series of preferred shares may be fixed by the Board and may materially limit and/or qualify the rights of holders of the Fund’s common shares. If the Fund’s Board determines that it may be advantageous to the holders of the Fund’s common shares for the Fund to utilize additional leverage, the Fund may issue additional series of fixed rate preferred shares. Any fixed rate preferred shares issued by the Fund will pay distributions at a fixed rate. The Fund will not issue additional series of auction rate preferred shares in a public offering pursuant to this Prospectus. Leverage creates a greater risk of loss as well as a potential for more gains for the common shares than if

leverage were not used. See “Risk Factors and Special Considerations—Special Risk Factors to Holders of Common Shares—Leverage Risk.” The Fund may also determine in the future to issue other forms of senior securities, such as securities representing debt, subject to the limitations of the 1940 Act. The Fund may also engage in investment management techniques which will not be considered senior securities if the Fund establishes a segregated account with cash or other liquid assets or sets aside assets on the accounting records equal to the Fund’s obligations in respect of such techniques. The Fund may also borrow money, to the extent permitted by the 1940 Act. See “Investment Objective and Policies—Certain Investment Practices” in the Prospectus.

Dividends and Distributions

Distributions on fixed rate preferred shares, at the applicable annual rate of the per share liquidation preference, are cumulative from the original issue date and are payable, when, as and if declared by the Board, out of funds legally available therefor. The holders of auction

rate preferred shares are entitled to receive cash distributions, based on the applicable per share liquidation preference, that vary from dividend period to dividend period.

A portion of the Fund’s common share distributions for many of its fiscal years has included a return of capital. During the fiscal year ended December 31, 2018, the Fund made distributions of $1.32 per common share, approximately $0.0204 of which constituted a return

of capital. When the Fund makes distributions consisting of returns of capital, such distributions may further decrease the Fund’s total assets and, therefore have the likely effect of increasing the Fund’s expense ratio as the Fund’s fixed expenses will become a larger percentage of the Fund’s average net assets. In addition, in order to make such distributions, the Fund may have to sell a portion of its investment portfolio at a time when independent investment judgment may not dictate such action. These effects could have a negative impact on the prices investors receive when they sell shares of the Fund.

Indebtedness

Use of Proceeds

The Fund may use the net proceeds from the offering to call, redeem or repurchase shares of one or more of its Series A Preferred, Series B Auction Market Preferred, Series C Auction Market Preferred, Series D Preferred or Series E Auction Rate Preferred. The Series G Preferred Shares generally may not be called for redemption at the option of the Fund prior to July 1, 2021. The Fund reserves the right, however, to redeem the Series G Preferred Shares at any time if it is necessary, in the judgment of the Board, to maintain its status as a

RIC under Subchapter M of the Code. The distribution rates on the Series A Preferred, Series D Preferred and Series G Preferred are 5.875%, 6.00% and 5.25%, respectively. Distributions on the Series B Auction Market Preferred, Series C Auction Market Preferred and Series E Auction Rate Preferred accumulate at a variable rate set at a weekly auction. As of April 16, 2019, April 18, 2019 and April 17, 2019, the distribution rates on the Series B Auction Market Preferred, Series C Auction Market Preferred and Series E Auction Rate Preferred, respectively, were 3.913%, 3.911% and 6.034%, respectively.

Exchange Listing

Risk Factors and Special Considerations

Distribution Risk for Equity Income Securities. In selecting equity income securities in which the Fund will invest, the Investment Adviser will consider the issuer’s history of making regular periodic distributions (i.e., dividends) to its equity holders. An issuer’s history of paying dividends, however, does not guarantee that the issuer will continue to pay dividends in the future. The dividend income stream associated with equity income securities generally is not guaranteed and will be subordinate to payment obligations of the issuer on its debt and other liabilities. Accordingly, in the event the issuer does not realize sufficient income in a particular period both to service its liabilities and to pay dividends on its equity securities, it may forgo paying dividends on its equity securities. In addition, because in most instances issuers are not obligated to make periodic distributions to the holders of their equity securities, such distributions or dividends generally may be discontinued at the issuer’s discretion. Dividend producing equity securities, in particular those whose market price is closely related to their yield, may exhibit greater sensitivity to interest rate changes. The Fund’s investments in dividend producing equity securities may also limit its potential for appreciation during a broad market advance. The prices of dividend producing equity securities can be highly volatile. Investors should not assume that the Fund’s investments in these securities will necessarily reduce the volatility of the Fund’s NAV or provide “protection,” compared to other types of equity securities, when markets perform poorly. See “Risk Factors

and Special Considerations—General Risks—Distribution Risk for Equity Income Securities” in the Prospectus.

Interest Rate Risk. The market value of bonds and other fixed-income or dividend-paying securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other income- or dividend-paying securities will increase as interest rates fall and decrease as interest rates rise. This effect is generally more pronounced for fixed rate securities than for securities whose income rate is periodically reset. The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low interest rates. Recently, there have been some modest signs of inflationary price movements. There is a possibility that interest rates may rise, which would likely drive down the prices of income- or dividend-paying securities. Further, while longer term fixed rate securities may pay higher interest rates than shorter term securities, longer term fixed rate securities, like fixed rate securities, also tend to be more sensitive to interest rate changes and, accordingly, tend to experience larger changes in value as a result of interest rate changes. An increase in market interest rates will also generally result in a decrease in the price of any of the Fund’s outstanding preferred shares.

Issuer Risk. Issuer risk is the risk that the value of an income- or dividend-paying security may decline for a number of reasons which directly relate to the issuer, such as management performance, financial leverage, reduced demand for the issuer’s goods and services, historical and prospective earnings of the issuer and the value of the assets of the issuer.

Credit Risk. Credit risk is the risk that one or more income- or dividend-paying securities in the Fund’s portfolio will decline in price or fail to pay interest/distributions or principal when due because the issuer of the security experiences a decline in its financial status. Credit risk is increased when a portfolio security is downgraded or the perceived creditworthiness of the issuer deteriorates.

Prepayment Risk. Prepayment risk is the risk that during periods of declining interest rates, borrowers may exercise their option to prepay principal earlier than scheduled. For income- or dividend-paying securities, such payments often occur during periods of declining interest rates, forcing the Fund to reinvest in lower yielding securities, resulting in a possible decline in the Fund’s income and distributions to shareholders.

Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if the Fund invests the

proceeds from matured, traded or called fixed income securities at market interest rates that are below the Fund portfolio’s current earnings rate.

Duration and Maturity Risk. The Fund may incur costs in seeking to adjust the portfolio average duration or maturity. In comparison to maturity (which is the date on which the issuer of a debt instrument is obligated to repay the principal amount), duration is a measure of the price volatility of a debt instrument as a result of changes in market rates of interest, based on the weighted average timing of the instrument’s expected principal and interest payments. Specifically, duration measures the anticipated percentage change in net asset value (“NAV”) that is expected for every percentage point change in interest rates. The two have an inverse relationship. Duration can be a useful tool to estimate anticipated price changes to a fixed pool of income securities associated with changes in interest rates. Duration differs from maturity in that it takes into account a security’s yield, coupon payments and its principal payments in addition to the amount of time until the security matures. As the value of a security changes over time, so will its duration. There can be no assurance that the Investment Adviser’s assessment of current and projected market conditions will be correct or that any strategy to adjust duration or maturity will be successful at any given time.

Non-Investment Grade Securities. The Fund may invest in securities rated below investment grade by recognized statistical rating agencies or unrated securities of comparable quality. The prices of these lower grade securities are more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn, than are the prices of higher grade securities. Securities of below investment grade quality—those securities rated below Baa by Moody’s or below BBB by S&P—are predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal when due and therefore involve a greater risk of default and are commonly referred to as “junk bonds” or “high yield securities.”

See “Risk Factors and Special Considerations—General Risks—Non-Investment Grade Securities” in the Prospectus.

The events surrounding negotiations regarding the U.S. federal government debt ceiling and deficit reduction could adversely affect the Fund’s ability to achieve its investment objective. In 2011, S&P

lowered its long term sovereign credit rating on the U.S. to “AA+” from “AAA.” The downgrade by S&P increased volatility in both stock and bond markets, resulting in higher interest rates and higher Treasury yields, and increased the costs of all kinds of debt. Repeat occurrences of similar events could have significant adverse effects on the U.S. economy generally and could result in significant adverse impacts on issuers of securities held by the Fund itself. The Investment Adviser cannot predict the effects of similar events in the future on the U.S. economy and securities markets or on the Fund’s portfolio. The Investment Adviser monitors developments and seeks to manage the Fund’s portfolio in a manner consistent with achieving the Fund’s investment objective, but there can be no assurance that it will be successful in doing so and the Investment Adviser may not timely anticipate or manage existing, new or additional risks, contingencies or developments. See “Risk Factors and Special Considerations—General Risks—U.S. Government Securities and Credit Rating Downgrade Risk” in the Prospectus.

The Fund may invest in companies whose securities are denominated or quoted in currencies other than U.S. dollars or have significant

operations or markets outside of the United States. In such instances, the Fund will be exposed to currency risk, including the risk of fluctuations in the exchange rate between U.S. dollars (in which the Fund’s shares are denominated) and such foreign currencies, the risk of currency devaluations and the risks of non-exchangeability and blockage. As non-U.S. securities may be purchased with and payable in currencies of countries other than the U.S. dollar, the value of these assets measured in U.S. dollars may be affected favorably or unfavorably by changes in currency rates and exchange control regulations. Fluctuations in currency rates may adversely affect the ability of the Investment Adviser to acquire such securities at advantageous prices and may also adversely affect the performance of such assets.

The Fund’s leveraged capital structure creates special risks not associated with unleveraged funds having a similar investment

objective and policies. These include the possibility of greater loss and the likelihood of higher volatility of the net asset value of the Fund and the asset coverage for the preferred shares. Such volatility may increase the likelihood of the Fund having to sell investments in order to meet its obligations to make distributions on the preferred shares or principal or interest payments on debt securities, or to redeem preferred shares or repay debt, when it may be disadvantageous to do so. The Fund’s use of leverage may require it to sell portfolio investments at inopportune times in order to raise cash to redeem preferred shares or otherwise de-leverage so as to maintain required asset coverage amounts or comply with the mandatory redemption terms of any outstanding preferred shares. The use of leverage magnifies both the favorable and unfavorable effects of price movements in the investments made by the Fund. To the extent that the Fund employs leverage in its investment operations, the Fund is subject to substantial risk of loss. The Fund cannot assure you that borrowings or the issuance of preferred shares will result in a higher yield or return to the holders of the common shares. Also, since the Fund utilizes leverage, a decline in net asset value could affect the ability of the Fund to make common share distributions and such a failure to make distributions could result in the Fund ceasing to qualify as a RIC under the Code.

In addition, the Fund pays (and the holders of common shares bear) all costs and expenses relating to the issuance and ongoing

maintenance of the preferred shares or notes, including any additional advisory fees on the incremental assets attributable to such preferred shares or notes. Holders of preferred shares and notes may have different interests than holders of common shares and at times may have disproportionate influence over the Fund’s affairs. As provided in the 1940 Act and subject to certain exceptions, the Fund may issue senior securities (which may be stock, such as preferred shares, and/or securities representing debt, such as notes) only if immediately after such issuance the value of the Fund’s total assets, less certain ordinary course liabilities, exceeds 300% of the amount of the debt outstanding and exceeds 200% of the amount of preferred shares and debt outstanding, which is referred to as the “asset coverage” required by the 1940 Act. In the event the Fund fails to maintain an asset coverage of 100% for any notes outstanding for certain periods of time, the 1940 Act requires that either an event of default be declared or that the holders of such notes have the right to elect a majority of the Fund’s Trustees until asset coverage recovers to 110%. In addition, holders of preferred shares, voting separately as a single class, have the right to elect two members of the Board at all times and in the event dividends become in arrears for two full years would have the right (subject to the rights of noteholders) to elect a majority of the Trustees until the arrearage is completely eliminated. In addition, preferred shareholders have class voting rights on certain matters, including changes in fundamental investment restrictions and conversion of the Fund to open-end status, and accordingly can veto any such changes. Further, interest on notes will be payable when due as described in a Prospectus Supplement and if the Fund does not pay interest when due, it will trigger an event of default and the Fund expects to be restricted from declaring dividends and making other distributions with respect to common shares and preferred shares. Upon the occurrence and continuance of an event of default, the holders of a majority in principal amount of a series of outstanding notes or the trustee will be able to declare the principal amount of that series of notes immediately due and payable upon written notice to the Fund. The 1940 Act also generally restricts the Fund from declaring distributions on, or repurchasing, common or preferred shares unless notes have an asset coverage of 300% (200% in case of declaring distributions on preferred shares). The Fund’s common shares are structurally subordinated as to income and residual value to any preferred shares or notes in the Fund’s capital structure, in terms of priority to income and payment in liquidation. See “Risk Factors and Special Considerations—Special Risks to Holders of Common Shares—Leverage Risk” and “Description of the Securities—Preferred Shares—Asset Maintenance Requirements” and “Description of the Securities—Notes—Limitations” in the Prospectus.

Market Discount Risk. The Fund is a diversified, closed-end management investment company. Whether investors will realize gains or losses upon the sale of additional securities of the Fund will

depend upon the market price of the securities at the time of sale, which may be less or more than the Fund’s net asset value per share or the liquidation value of any Fund preferred shares issued. The Fund cannot predict whether any such securities will trade at, below or above net asset value or at, below or above their public offering price. The risk of a market price discount from net asset value is separate and in addition to the risk that net asset value itself may decline. The Fund’s securities are designed primarily for long term investors, and investors in the shares should not view the Fund as a vehicle for trading purposes. See “Risk Factors and Special Considerations—General Risks—Market Discount Risk” in the Prospectus.

Special Risks to Holders of Auction Rate Preferred Shares. Holders of auction rate preferred shares may not be able to sell their auction rate preferred shares at an auction if the auction fails, i.e., if more auction rate preferred shares are offered for sale than there are buyers for those shares. If you try to sell your auction rate preferred shares between auctions, you may not be able to sell them for their liquidation preference per share or such amount per share plus accumulated dividends. Since February 2008 all of the auctions of our Series B Preferred, Series C Preferred, and Series E Preferred have failed. Most auction rate preferred share auctions have been unable to hold successful auctions and holders of such shares have suffered reduced liquidity. Holders of our auction rate preferred have continued to receive their dividends on the auction rate preferred shares at the maximum rate determined by reference to short term rates, rather than at a price set by auction. At present, the maximum rate for Series B Auction Market Preferred and Series C Auction Market Preferred is equal to the greater of (a) 150% of or (b) 150 bps over the 7-day LIBOR, and equal to the greater of (a) 250% of or (b) 250 bps over the 7-day LIBOR for Series E Preferred. A failed auction is not a default and the Fund has no obligation to redeem its auction rate preferred shares because the auctions continue to fail. There can be no assurance that liquidity will improve. There appears to be a secondary market in certain auction market preferred issues, although the Fund is not aware whether there is or will be an active

trading market for the Fund’s auction rate preferred shares. See “Risk Factors and Special Considerations—Special Risks to Holders of Auction Rate Preferred Shares” in the Prospectus.

Credit Quality Ratings. The Fund may obtain credit quality ratings for its preferred shares or notes; however, it is not required to do so and

may issue preferred shares or notes without any rating. If rated, the Fund does not impose any minimum rating necessary to issue such preferred shares or notes. In order to obtain and maintain attractive credit quality ratings for preferred shares or borrowings, if desired, the Fund’s portfolio must satisfy over-collateralization tests established by the relevant rating agencies. These tests are more difficult to satisfy to the extent the Fund’s portfolio securities are of lower credit quality, longer maturity or not diversified by issuer and industry. These guidelines could affect portfolio decisions and may be more stringent than those imposed by the 1940 Act. A rating by a rating agency does not eliminate or necessarily mitigate the risks of investing in our preferred shares or notes, and a rating may not fully or accurately reflect all of the securities’ credit risks. A rating does not address liquidity or any other market risks of the securities being rated. A rating agency could downgrade the rating of our preferred shares or notes, which may make such securities less liquid in the secondary market. If a rating agency downgrades the rating assigned to preferred shares or notes, we may alter our portfolio or redeem the preferred shares or notes under certain circumstances. See “Risk Factors and Special Considerations—Special Risks to Holders of Notes and Preferred Shares—Credit Quality Ratings” in the Prospectus.

Dilution. Shareholders who do not exercise their subscription rights may, at the completion of such an offering, own a smaller proportional interest in the Fund than if they exercised their subscription rights. As a result of such an offering, a shareholder may experience dilution in net asset value per share if the subscription price per share is below the net asset value per share on the expiration date. If the subscription price per share is below the net asset value per share of the Fund’s shares on the expiration date, a shareholder will experience an immediate dilution of the aggregate net asset value of such shareholder’s shares if the shareholder does not participate in such an offering and the shareholder will experience a reduction in the net asset value per share of such shareholder’s shares whether or not the shareholder participates in such an offering. The Fund cannot

state precisely the extent of this dilution (if any) if the shareholder does not exercise such shareholder’s subscription rights because the Fund does not know what the net asset value per share will be when the offer expires or what proportion of the subscription rights will be exercised.

Management and Fees

Because the investment advisory fees are based on a percentage of net assets, which includes assets attributable to the Fund’s use of leverage (but excludes assets attributable to the certain of the Fund’s existing preferred shares when such shares are subject to the fee reduction

described in the section entitled “Management of the Fund—Investment Advisory and Administrative Arrangements” in the Prospectus), the Investment Adviser may have a conflict of interest in the input it provides to the Board regarding whether to use or increase the Fund’s use of leverage. The Board bases its decision, with input from the Investment Adviser, regarding whether and how much leverage to use for the Fund on its assessment of whether such use of leverage is in the best interests of the Fund, and the Board seeks to manage the Investment Adviser’s potential conflict of interest by retaining the final decision on these matters and by periodically reviewing the Fund’s performance and use of leverage. See “Management of the Fund—Investment Advisory and Administrative Arrangements” in the Prospectus.

Repurchase of Common Shares

Anti-Takeover Provisions

Custodian, Transfer Agent, Auction Agent and Dividend Disbursing Agent

State Street Bank and Trust Company (“State Street” or the “Custodian”), located at State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111, serves as the custodian of the

Fund’s assets pursuant to a custody agreement. Under the custody agreement, the Custodian holds the Fund’s assets in compliance with the 1940 Act. For its services, the Custodian receives a monthly fee based upon, among other things, the average value of the total assets of the Fund, plus certain charges for securities transactions.