Sec Form 4 Filing - GV 2019 GP, L.L.C. @ Prime Medicine, Inc. - 2023-05-18

FORM 4 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) 05/18/2023 (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 Common Stock 05/18/2023 S( 1 ) 13,076 D $ 13.0086 ( 2 ) 10,722,248 I By GV 2019, L.P. ( 3 ) Common Stock 05/18/2023 J( 4 ) 14,022 D $ 0 10,708,226 I By GV 2019, L.P. ( 3 ) Common Stock 05/18/2023 S( 1 ) 14,022 D $ 13.0631 ( 5 ) 0 I By Alphabet Holdings LLC ( 6 ) Common Stock 05/19/2023 J( 4 ) 63,212 D $ 0 10,645,014 I By GV 2019, L.P. ( 3 ) Common Stock 05/19/2023 S( 1 ) 63,212 D $ 13.875 ( 7 ) 0 I By Alphabet Holdings LLC ( 6 ) Common Stock 1,762,440 I By GV 2021, L.P. ( 8 )

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

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 X GV 2021 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2021, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X Alphabet Inc. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X Signatures /s/ Inga Goldbard, General Counsel of GV 2019 GP, L.L.C. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2019 GP, L.P. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2019, L.P. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021 GP, L.L.C. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021 GP, L.P. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, General Counsel of GV 2021, L.P. 05/22/2023 Signature of Reporting Person Date /s/ Inga Goldbard, Attorney-in-fact of Alphabet Inc. 05/22/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )This transaction was entered into pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on April 6, 2023. ( 2 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.00 to $13.05, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the U.S. Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote 2 and in footnotes 5 and 7 of this Form 4. ( 3 )The securities reported in this row are directly beneficially owned by GV 2019, L.P. (the "2019 Partnership"). The general partner of the 2019 Partnership is GV 2019 GP, L.P. (the "2019 GP"). The general partner of the 2019 GP is GV 2019 GP, L.L.C. ("GV 2019 LLC"). The sole member of GV 2019 LLC is Alphabet Holdings LLC ("Alphabet Holdings"). The sole member of Alphabet Holdings is XXVI Holdings Inc. ("XXVI"). The controlling stockholder of XXVI is Alphabet Inc. Each of the 2019 GP, GV 2019 LLC, Alphabet Holdings, XXVI, and Alphabet Inc. may 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 "Act")) the securities directly beneficially owned by the 2019 Partnership. Each of the aforementioned parties disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 4 )The reported transaction represents a pro rata in-kind distribution, for no consideration, by the 2019 Partnership to its partners, which resulted in all of the securities reported in Column 4 of this row being distributed to the direct ownership of the 2019 Partnership's affiliate, Alphabet Holdings. The aforementioned distribution was made in accordance with the exemptions afforded pursuant to Rules 16a-13 and/or 16a-9 promulgated under the Securities Exchange Act of 1934, as amended, and pursuant to a Rule 10b5-1 plan adopted by the 2019 Partnership on April 6, 2023. ( 5 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.02 to $13.10, inclusive. ( 6 )The securities reported in this row were directly beneficially owned by Alphabet Holdings at the time of sale. The sole member of Alphabet Holdings is XXVI. The controlling stockholder of XXVI is Alphabet Inc. Each of XXVI and Alphabet Inc. may be deemed to indirectly beneficially own (as the term is defined in Rule 13d-3 of the Act) securities directly beneficially owned by Alphabet Holdings. Each of the aforementioned entities disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 7 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $13.30 to $14.03, inclusive. ( 8 )The securities reported in this row are directly beneficially owned by GV 2021, L.P. (the "2021 Partnership"). The general partner of the 2021 Partnership is GV 2021 GP, L.P. (the "2021 GP"). The general partner of the 2021 GP is GV 2021 GP, L.L.C. ("GV 2021 LLC"). The sole member of GV 2021 LLC is Alphabet Holdings. The sole member of Alphabet Holdings is XXVI. The controlling stockholder of XXVI is Alphabet Inc. Each of the 2021 GP, GV 2021 LLC, Alphabet Holdings, XXVI, and Alphabet Inc. may be deemed to indirectly beneficially own (as the term is defined in Rule 13d-3 of the Act) the securities directly beneficially owned by the 2021 Partnership. Each of the aforementioned parties 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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