<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

                           --------------------------

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934

                            -------------------------

       Date of Report (Date of earliest event reported): November 15, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                     (ON BEHALF OF PPLUS TRUST SERIES SPR-1)
             (Exact name of registrant as specified in its charter)

         DELAWARE                 001-31912                    13-3891329
     (State or other            (Commission                (I. R. S. Employer
     jurisdiction  of            File Number)              Identification No.)
      incorporation)

  WORLD FINANCIAL CENTER,                                         10080
    NEW YORK, NEW YORK                                         (Zip Code)
   (Address of principal
    executive offices)
                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT


SECTION 1.        REGISTRANT'S BUSINESS AND OPERATIONS

                  Not applicable.

SECTION 2.        FINANCIAL INFORMATION

                  Not applicable.

SECTION 3.        SECURITIES AND TRADING MARKETS

                  Not applicable.

SECTION 4.        MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

                  Not applicable.

SECTION 5.        CORPORATE GOVERNANCE AND MANAGEMENT

                  Not applicable.
<PAGE>

SECTION 6.        [RESERVED]



SECTION 7.        REGULATION FD

                  Not applicable.

SECTION 8.        OTHER EVENTS

     ITEM 8.01    OTHER EVENTS

       99.1       Distribution to holders of the PPLUS Trust
                  Certificates Series SPR-1 on November 15, 2005.

                           For information with respect to the
                  underlying securities held by PPLUS Trust Series
                  SPR-1, please refer to Sprint Corporation's
                  (Commission file number 001-04721) periodic reports,
                  including annual reports on Form 10-K, quarterly
                  reports on Form 10-Q and current reports on Form 8-K,
                  and other information on file with the Securities and
                  Exchange Commission (the "SEC"). You can read and
                  copy these reports and other information at the
                  public reference facilities maintained by the SEC at
                  Room 1580, 100 F Street, NE, Washington, D.C. 20549.
                  You may obtain copies of this material for a fee by
                  writing to the SEC's Public Reference Section of the
                  SEC at 100 F Street, NE, Washington, D.C. 20549. You
                  may obtain information about the operation of the
                  Public Reference Room by calling the SEC at
                  1-800-SEC-0330. You can also access some of this
                  information electronically by means of the SEC's
                  website on the Internet at http://www.sec.gov, which
                  contains reports, proxy and information statements
                  and other information that the underlying securities
                  issuer has filed electronically with the SEC.

                           Although we have no reason to believe the
                  information concerning the underlying securities, the
                  underlying guarantee, the underlying securities
                  issuer or the underlying securities guarantor
                  contained in the underlying securities guarantor's
                  Exchange Act reports is not reliable, neither the
                  depositor nor the trustee participated in the
                  preparation of such documents or made any due
                  diligence inquiry with respect to the information
                  provided therein. No investigation with respect to
                  the underlying securities issuer or the underlying
                  securities guarantor (including, without limitation,
                  no investigation as to their financial condition or
                  creditworthiness) or of the underlying securities or
                  the underlying guarantee has been made. You should
                  obtain and evaluate the same information concerning
                  the underlying securities issuer and the underlying
                  securities guarantor as you would obtain and evaluate
                  if your investment were directly in the underlying
                  securities or in other securities issued by the
                  underlying securities issuer or the underlying
                  securities guarantor. There can be no assurance that
                  events affecting the underlying securities and the
                  underlying guarantee or the underlying securities
                  issuer and the underlying securities guarantor have
                  not occurred or have not yet been publicly disclosed
                  which would affect the accuracy or completeness of
                  the publicly available documents described above.

<PAGE>

SECTION 9.        FINANCIAL STATEMENTS AND EXHIBITS

     ITEM 9.01    FINANCIAL STATEMENTS AND EXHIBITS

         (a)      Financial statements of business acquired.

                  Not Applicable.

         (b)      Pro forma financial information.

                  Not Applicable.

         (c)      Exhibits.

                     99.1       Trustee's report in respect of
                                the November 15, 2005 distribution to
                                holders of the PPLUS Trust Certificates
                                Series SPR-1.



                                   SIGNATURES

         Pursuant to the requirements of the Securities Exchange Act of 1934,
         the registrant has duly caused this report to be signed on its behalf
         by the undersigned, hereunto duly authorized.


                                             MERRILL LYNCH DEPOSITOR, INC.

         Date:                               By:    /s/ Stephan Kuppenheimer
                                                     --------------------------
                                             Name:  Stephan Kuppenheimer
                                             Title: President




<PAGE>



                                            EXHIBIT INDEX


         99.1              Trustee's report in respect of the November 15,
                           2005 distribution to holders of the PPLUS Trust
                           Certificates Series SPR-1.
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SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

                           --------------------------

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934

                            -------------------------

       Date of Report (Date of earliest event reported): November 15, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                     (ON BEHALF OF PPLUS TRUST SERIES SPR-1)
             (Exact name of registrant as specified in its charter)

         DELAWARE                 001-31912                    13-3891329
     (State or other            (Commission                (I. R. S. Employer
     jurisdiction  of            File Number)              Identification No.)
      incorporation)

  WORLD FINANCIAL CENTER,                                         10080
    NEW YORK, NEW YORK                                         (Zip Code)
   (Address of principal
    executive offices)
                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT

SECTION 1.        REGISTRANT'S BUSINESS AND OPERATIONS

                  Not applicable.

SECTION 2.        FINANCIAL INFORMATION

                  Not applicable.

SECTION 3.        SECURITIES AND TRADING MARKETS

                  Not applicable.

SECTION 4.        MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

                  Not applicable.

SECTION 5.        CORPORATE GOVERNANCE AND MANAGEMENT

                  Not applicable.
SECTION 6.        [RESERVED]

SECTION 7.        REGULATION FD

                  Not applicable.

SECTION 8.        OTHER EVENTS

     ITEM 8.01    OTHER EVENTS

       99.1       Distribution to holders of the PPLUS Trust
                  Certificates Series SPR-1 on November 15, 2005.

                           For information with respect to the
                  underlying securities held by PPLUS Trust Series
                  SPR-1, please refer to Sprint Corporation's
                  (Commission file number 001-04721) periodic reports,
                  including annual reports on Form 10-K, quarterly
                  reports on Form 10-Q and current reports on Form 8-K,
                  and other information on file with the Securities and
                  Exchange Commission (the "SEC"). You can read and
                  copy these reports and other information at the
                  public reference facilities maintained by the SEC at
                  Room 1580, 100 F Street, NE, Washington, D.C. 20549.
                  You may obtain copies of this material for a fee by
                  writing to the SEC's Public Reference Section of the
                  SEC at 100 F Street, NE, Washington, D.C. 20549. You
                  may obtain information about the operation of the
                  Public Reference Room by calling the SEC at
                  1-800-SEC-0330. You can also access some of this
                  information electronically by means of the SEC's
                  website on the Internet at http://www.sec.gov, which
                  contains reports, proxy and information statements
                  and other information that the underlying securities
                  issuer has filed electronically with the SEC.

                           Although we have no reason to believe the
                  information concerning the underlying securities, the
                  underlying guarantee, the underlying securities
                  issuer or the underlying securities guarantor
                  contained in the underlying securities guarantor's
                  Exchange Act reports is not reliable, neither the
                  depositor nor the trustee participated in the
                  preparation of such documents or made any due
                  diligence inquiry with respect to the information
                  provided therein. No investigation with respect to
                  the underlying securities issuer or the underlying
                  securities guarantor (including, without limitation,
                  no investigation as to their financial condition or
                  creditworthiness) or of the underlying securities or
                  the underlying guarantee has been made. You should
                  obtain and evaluate the same information concerning
                  the underlying securities issuer and the underlying
                  securities guarantor as you would obtain and evaluate
                  if your investment were directly in the underlying
                  securities or in other securities issued by the
                  underlying securities issuer or the underlying
                  securities guarantor. There can be no assurance that
                  events affecting the underlying securities and the
                  underlying guarantee or the underlying securities
                  issuer and the underlying securities guarantor have
                  not occurred or have not yet been publicly disclosed
                  which would affect the accuracy or completeness of
                  the publicly available documents described above.
SECTION 9.        FINANCIAL STATEMENTS AND EXHIBITS

     ITEM 9.01    FINANCIAL STATEMENTS AND EXHIBITS

         (a)      Financial statements of business acquired.

                  Not Applicable.

         (b)      Pro forma financial information.

                  Not Applicable.

         (c)      Exhibits.

                     99.1       Trustee's report in respect of
                                the November 15, 2005 distribution to
                                holders of the PPLUS Trust Certificates
                                Series SPR-1.

                                   SIGNATURES

         Pursuant to the requirements of the Securities Exchange Act of 1934,
         the registrant has duly caused this report to be signed on its behalf
         by the undersigned, hereunto duly authorized.

                                             MERRILL LYNCH DEPOSITOR, INC.

         Date:                               By:    /s/ Stephan Kuppenheimer
                                                     --------------------------
                                             Name:  Stephan Kuppenheimer
                                             Title: President
EXHIBIT INDEX

         99.1              Trustee's report in respect of the November 15,
                           2005 distribution to holders of the PPLUS Trust
                           Certificates Series SPR-1.