Sec Form 3 Filing - GV 2019 GP, L.L.C. @ Prime Medicine, Inc. - 2022-10-19

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 GV 2019 GP, L.L.C. 2. Issuer Name and Ticker or Trading Symbol Prime Medicine, Inc. [ PRME] 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) 1600 AMPHITHEATRE PARKWAY 3. Date of Earliest Transaction (MM/DD/YY) 10/19/2022 (Street) MOUNTAIN VIEW, CA94043 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

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 Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 10,722,248 I By GV 2019, L.P.( 2 ) Series B Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,762,440 I By GV 2021, L.P.( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other GV 2019 GP, L.L.C. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2019 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2019, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2021 GP, L.L.C. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 Member of a 10% Group GV 2021 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 Member of a 10% Group GV 2021, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 Member of a 10% Group Alphabet Inc. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 Member of a 10% Group Signatures /s/ Inga Goldbard, General Counsel of GV 2019 GP, L.L.C. 10/19/2022 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2019 GP, L.P. 10/19/2022 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2019, L.P. 10/19/2022 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021 GP, L.L.C. 10/19/2022 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021 GP, L.P. 10/19/2022 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021, L.P. 10/19/2022 Signature of Reporting Person Date /s/ Kathryn W. Hall, Assistant Secretary of Alphabet Inc. 10/19/2022 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares of Series A Convertible Preferred Stock and Series B Convertible Preferred Stock (together, the "Preferred Stock") are convertible into Common Stock on a one-for-3.10880 basis at any time at the option of the holder, and will automatically convert into the number of shares shown in Column 3 immediately prior to the closing of the Issuer's initial public offering. The Preferred Stock has no expiration date. ( 2 )The reported securities are held directly by GV 2019, L.P. GV 2019 GP, L.P. ("GV 2019 GP"), the general partner of GV 2019, L.P., GV 2019 GP, L.L.C. ("GV 2019 LLC"), the general partner of GV 2019 GP, L.P., Alphabet Holdings LLC ("Alphabet Holdings"), the sole member of GV 2019 GP, L.L.C., XXVI Holdings Inc. ("XXVI"), the sole member of Alphabet Holdings LLC, and Alphabet Inc. ("Alphabet"), the controlling stockholder of XXVI Holdings Inc. may each be deemed to indirectly beneficially own (as the term is defined in Rule 13d-3 of the Securities Exchange Act of 1934, as amended (the "Exchange Act")) the securities directly beneficially owned by GV 2019, L.P. Each of GV 2019 GP, GV 2019 LLC, Alphabet Holdings, XXVI and Alphabet disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 3 )The reported securities are held directly by GV 2021, L.P. GV 2021 GP, L.P. ("GV 2021 GP"), the general partner of GV 2021, L.P., GV 2021 GP, L.L.C. ("GV 2021 LLC"), the general partner of GV 2021 GP, L.P., Alphabet Holdings, the sole member of GV 2021 GP, L.L.C., XXVI, the sole member of Alphabet Holdings, and Alphabet, the controlling stockholder of XXVI, may each be deemed to indirectly beneficially own (as such term is defined in Rule 13d-3 of the Exchange Act) the securities directly beneficially owned by GV 2021, L.P. Each of GV 2021 GP, GV 2021 LLC, Alphabet Holdings, XXVI and Alphabet, disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein.

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

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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