<PAGE>   1
                                                                   EXHIBIT 3.112

          [STATE OF DELAWARE OFFICE OF SECRETARY OF STATE LETTERHEAD]

                                                                          PAGE 1

     I, MICHAEL HARKINS, SECRETARY OF STATE OF THE STATE OF DELAWARE DO HEREBY 
CERTIFY THE ATTACHED IS A TRUE AND CORRECT COPY OF THE CERTIFICATE OF 
INCORPORATION OF E.R. ACQUISITION, INC. FILED IN THIS OFFICE ON THE SIXTEENTH 
DAY OF JULY, A.D. 1990, AT 1 O'CLOCK P.M.

                           /    /    /    /    /    /



                              RECEIVED FOR RECORD
                               Jul. 18 A.D. 1990

                            /s/ illegible signature
                                    RECORDER

                         $3.00 STATE DOCUMENT FEE PAID

[SEAL OF DEPT. OF STATE,
OFFICE OF THE SECRETARY 
OF STATE, DELAWARE]

750197007                                    /s/ Michael Harkins
                                             Michael Harkins, Secretary of State

                                                      AUTHENTICATION: 2727468
                                                                DATE: 07/16/1990
<PAGE>   2
                              CORPORATE FACT SHEET

                                                          As of January 14, 1991

                                                         CLIENT/MATTER 00608.117


NAME: Eastman Radio Sales, Inc. (formerly E.R. Acquisition, Inc.)

STATE & DATE OF INCORPORATION: Delaware - July 16, 1990

STATE(S) & DATE(S) OF QUALIFICATION: California, 11/28/90, Georgia, 11/28/90, 
New York, 11/28/90, Michigan, 11/30/90, Texas, 11/28/90, Washington, 11/28/90, 
Illinois - pending

REGISTERED AGENT & ADDRESS: The Prentice-Hall Corporation System, Inc., 32 
Loockerman Square, Suite L-100, Dover, Delaware 19901

FISCAL YEAR: 12/31
AUTHORIZED NUMBER OF SHARES: 1000
SHARES ISSUED: 100
PAR VALUE: $1.00
CLASS: Common

CORPORATE MINUTE BOOK KEPT BY: BATTLE FOWLER  X   CLIENT
                                             ---         ---

<TABLE>
<CAPTION>

                                                                     NUMBER
DIRECTORS           OFFICERS                     SHAREHOLDERS       OF SHARES
---------           --------                     ------------       ---------
<S>                 <C>                          <C>                <C>
Peter R. Goulazian  Kenneth J. Swetz --          Katz               100
James L. Greenwald   Chairman and Chief          Communications,    (Pledged
Arnold Sheiffer       Executive Officer          Inc.               to Citi-
Kenneth Swetz       James L. Greenwald --                           bank)
                     Senior Vice President
                      and Assistant Secretary
                    Peter R. Goulazian --
                     Senior Vice President
                    Arnold Sheiffer --
                     Senior Vice President,
                      Secretary and Treasurer
</TABLE>
<PAGE>   3
                          CERTIFICATE OF INCORPORATION

                                       OF

                             E.R. ACQUISITION, INC.


          THE UNDERSIGNED, in order to form a corporation for the purposes
herein stated, under and pursuant to the provisions of the General Corporation 
Law of the State of Delaware, does hereby certify as follows:

          FIRST:  The name of the corporation is E.R. Acquisition, Inc. 
(hereinafter called the "Corporation").

          SECOND:  The registered office of the Corporation is to be located at 
32 Loockerman Square, Suite L-100, Dover, County of Kent, Delaware 19901. The 
name of its registered agent at that address is The Prentice-Hall Corporation 
System, Inc.

          THIRD:  The purpose of the Corporation is to engage in any lawful act 
or activity, without limitation, for which a corporation may be organized under 
the General Corporation Law of the State of Delaware.

          FOURTH:  The total number of shares of all classes of stock which the 
Corporation is authorized to issue is One Thousand (1,000) shares, consisting 
entirely of Common Stock, all of which are of the par value of $1.00 per share.

          FIFTH:  The name and mailing address of the sole incorporator is:

          NAME                     ADDRESS
          ----                     -------
          Karen A. Foley           Battle Fowler
                                   280 Park Avenue
                                   New York, New York 10017

          SIXTH:  The election of directors need not be by written ballot 
unless the By-laws so provide.

          SEVENTH:  The Board of Directors of the Corporation is authorized and 
empowered from time to time in its discretion to make, alter, amend or repeal 
the By-laws of the Corporation, except as such power may be restricted or 
limited by the General Corporation Law of the State of Delaware.

          EIGHTH:  Whenever a compromise or arrangement is proposed between the 
Corporation and its creditors or any class of them and/or between the 
Corporation and its stockholders or any class of them, any court of equitable 
jurisdiction within the

<PAGE>   4
State of Delaware may, on the application in a summary way of the Corporation or
of any creditor or stockholder thereof or on the application of any receiver or
receivers appointed for the Corporation under the provisions of Section 291 of
Title 8 of the Delaware Code or on the application of trustees in dissolution or
of any receiver or receivers appointed for the Corporation under the provisions
of Section 279 of Title 8 of the Delaware Code, order a meeting of the creditors
or class of creditors, and/or of the stockholders or class of stockholders of
the Corporation, as the case may be, to be summoned in such manner as the said
court directs. If a majority in number representing three-fourths in value of
the creditors or class value of the creditors or class of creditors and/or of
the stockholders or class of stockholders of the Corporation, as the case may
be, agree to any compromise or arrangement and to any reorganization of the
Corporation as consequence of such compromise or arrangement, the said
compromise or arrangement and the said reorganization shall, if sanctioned by
the court to which the said application has been made, be binding on all
creditors or class of creditors, and/or all the stockholders or class of
stockholders of the Corporation, as the case may be, and also on the
Corporation.

          NINTH:  The Corporation reserves the right to amend, alter, change or 
repeal any provision contained in this Certificate of Incorporation in the 
manner now or hereafter prescribed by law, and all rights and powers conferred 
herein on stockholders, directors and officers are subject to this reserved 
power.

          TENTH:  The personal liability of the directors of the Corporation is 
hereby eliminated to the fullest extent permitted by paragraph (7) of 
subsection (b) of Section 102 of the General Corporation Law of the State of 
Delaware, as the same may be amended and supplemented.

          ELEVENTH:  The Corporation shall, to the fullest extent permitted by 
Section 145 of the General Corporation Law of the State of Delaware, as the 
same may be amended and supplemented, indemnify any and all persons who it 
shall have power to indemnify under said section from and against any and all 
of the expenses, liabilities or other matters referred to in or covered by said 
section, and the indemnification provided for herein shall not be deemed 
exclusive of any other rights to which those indemnified may be entitled under 
any By-laws, agreement, vote of stockholders or disinterested directors or 
otherwise, both as to action in his official capacity and as to action in any 
other capacity while holding such office, and shall continue as to a person who 
has ceased to be a director, officer, employee or


                                      -2-
<PAGE>   5

agent and shall inure to the benefit of the heirs, executors and administrators 
of such a person.

     IN WITNESS WHEREOF, I have hereunto set my hand this 16th day of July, 
1990.


                                             /s/ Karen A. Foley
                                             ----------------------
                                             Karen A. Foley, Sole Incorporator
                                             Battle Fowler
                                             180 Park Avenue
                                             New York, New York 10017



                                      -3-
<PAGE>   6
                                                                          PAGE 1

                               STATE OF DELAWARE


                                 [STATE EMBLEM]

                          OFFICE OF SECRETARY OF STATE

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

     I, MICHAEL HARKINS, SECRETARY OF STATE OF THE STATE OF DELAWARE DO HEREBY 
CERTIFY THE ATTACHED IS A TRUE AND CORRECT COPY OF THE CERTIFICATE OF AMENDMENT 
OF E.R. ACQUISITION, INC. FILED IN THIS OFFICE ON THE FIFTEENTH DAY OF AUGUST, 
A.D. 1990, AT 12:30 O'CLOCK P.M.



                              RECEIVED FOR RECORD
                               Aug. 17 A.D. 1990
                               -------        --

                              /s/ MICHAEL T. SCUSE
                                    RECORDER

[DEPARTMENT OF STATE
        EMBLEM]          $3.00 STATE DOCUMENT FEE PAID

750227056                                 /S/ MICHAEL HARKINS
                                          --------------------------------------
                                            Michael Harkins, Secretary of State


                                          AUTHENTICATION:    2762417
                              
                                                    DATE:    08/15/1990
<PAGE>   7
     STATE OF DELAWARE
    SECRETARY OF STATE
 DIVISION OF CORPORATIONS
FILED 12:30 P.M. 08/15/1990
   750227056 - 2236027

                                   750227056

                            CERTIFICATE OF AMENDMENT
                                       TO
                          CERTIFICATE OF INCORPORATION
                                       OF
                             E.R. ACQUISITION, INC.
                          -----------------------------
                             Adopted in Accordance
                                With Section 242
                                     of the
                            General Corporation Law
                                     of the
                               State of Delaware
                          -----------------------------

     The undersigned, on behalf of E.R. Acquisition, Inc., a corporation 
organized and existing under and by virtue of the General Corporation Law of 
the State of Delaware, does hereby certify:

     FIRST: That the name of the corporation is E.R. Acquisition, Inc. (the 
"Corporation").

     SECOND: That the Certificate of Incorporation of the Corporation was filed 
with the Secretary of State of the State of Delaware on July 16, 1990.

     THIRD: That the amendment set forth herein to the Certificate of 
Incorporation of the Corporation was duly authorized by the Board of Directors 
and Stockholders of the Corporation in accordance with the provisions of 
Section 242 of the General Corporation Law of the State of Delaware.

     FOURTH: That in lieu of a vote of stockholders on this amendment, written 
consent of the stockholders was given in accordance with the provisions of 
Section 228(a) of the General Corporation Law of the State of Delaware.

     FIFTH: That the amendment to the Certificate of Incorporation of the 
Corporation effected by this Certificate of Amendment is to change the name of 
the Corporation to: Eastman Radio Sales, Inc.
<PAGE>   8
     SIXTH: That to accomplish the foregoing amendment, Article First of the 
Certificate of Incorporation of the Corporation is hereby amended to read as 
follows:

          "FIRST: The name of the corporation is Eastman Radio Sales, Inc. 
(hereinafter called the "Corporation")."

     IN WITNESS WHEREOF, this Certificate has been signed this 15th day of 
August, 1990, and the undersigned hereby affirms, under penalties of perjury, 
that the statements made herein are true and correct.

                                        E.R. Acquisition, Inc.

                                        By: /s/ Kenneth J. Swetz
                                           ---------------------------------
                                           Name: Kenneth J. Swetz
                                           Title: President

                                 Attest By: /s/ James L. Greenwald
                                           ---------------------------------
                                        Name: James L. Greenwald
                                        Title: Assistant Secretary
<PAGE>   9
                               State of Delaware

                            [LOGO SEAL OF DELAWARE]

                          OFFICE OF SECRETARY OF STATE

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

     I, MICHAEL HARKINS, SECRETARY OF STATE OF THE STATE OF DELAWARE DO HEREBY 
CERTIFY THE ATTACHED IS A TRUE AND CORRECT COPY OF THE CERTIFICATE OF AMENDMENT 
OF E.R. ACQUISITION, INC. FILED IN THIS OFFICE ON THE FIFTEENTH DAY OF AUGUST, 
A.D. 1990, AT 12:30 O'CLOCK P.M.



[DELAWARE DEPARTMENT OF STATE SEAL]                 /s/ Michael Harkins
                                             -----------------------------------
                                             Michael Harkins, Secretary of State

                                             AUTHENTICATION: 2762416
    750227056                                          DATE: 08/15/1990