Sec Form 3 Filing - THIRD ROCK VENTURES LP @ CONSTELLATION PHARMACEUTICALS INC - 2018-07-18

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person THIRD ROCK VENTURES LP 2. Issuer Name and Ticker or Trading Symbol CONSTELLATION PHARMACEUTICALS INC [ CNST] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O THIRD ROCK VENTURES, LLC, 29 NEWBURY STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 07/18/2018 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 11,050 D ( 1 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series A Preferred Stock ( 2 ) ( 2 ) ( 2 ) Common Stock 999,180 D ( 1 ) Series B Preferred Stock ( 3 ) ( 3 ) ( 3 ) Common Stock 967,389 D ( 1 ) Series D Preferred Stock ( 4 ) ( 4 ) ( 4 ) Common Stock 98,683 D ( 1 ) Series E Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 266,934 D ( 1 ) Series E-1 Preferred Stock ( 6 ) ( 6 ) ( 6 ) Common Stock 282,308 D ( 1 ) Series F Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 90,840 D ( 1 ) Warrant (right to buy) $ 1.55 ( 8 ) 05/24/2021 Common Stock 51,032 D ( 1 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other THIRD ROCK VENTURES LP C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON, MA02116 X Third Rock Ventures GP, L.P. 29 NEWBURY STREET, 3RD FLOOR BOSTON, MA02116 X TRV GP, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON, MA02116 X LEVIN MARK J C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON, MA02116 X STARR KEVIN P C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON, MA02116 X Signatures /s/ Kevin Gillis, Chief Financial Officer of TRV GP, LLC, general partner of Third Rock Ventures GP, L.P., general partner of Third Rock Ventures, L.P. 07/18/2018 Signature of Reporting Person Date /s/ Kevin Gillis, Chief Financial Officer of TRV GP, LLC, general partner of Third Rock Ventures GP, L.P. 07/18/2018 Signature of Reporting Person Date /s/ Kevin Gillis, Chief Financial Officer of TRV GP, LLC 07/18/2018 Signature of Reporting Person Date /s/ Kevin Gillis by power of attorney for Mark Levin 07/18/2018 Signature of Reporting Person Date /s/ Kevin Gillis by power of attorney for Kevin Starr 07/18/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )These securities are directly held by Third Rock Ventures, L.P. ("TRV"). The general partner of TRV is Third Rock Ventures GP, L.P. ("TRV GP"). The general partner of TRV GP is TRV GP, LLC ("TRV GP LLC"). The individual managers of TRV GP LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP, TRV GP LLC, Levin, Starr and Tepper disclaims beneficial ownership of these shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares. ( 2 )The Series A Preferred Stock is convertible into Common Stock on a 11.009-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 3 )The Series B Preferred Stock is convertible into Common Stock on a 11.009-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 4 )The Ser ies D Preferred Stock is convertible into Common Stock on a 11.009-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 5 )The Series E Preferred Stock is convertible into Common Stock on a 8.56256-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 6 )The Series E-1 Preferred Stock is convertible into Common Stock on a 11.009-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 7 )The Series F Preferred Stock is convertible into Common Stock on a 11.009-for-one basis into the number of shares of Common Stock shown in Column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 8 )The warrant was fully exercisable upon grant.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

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