GV 2019 GP, L.L.C. - 20 Jun 2023 Form 4 Insider Report for Prime Medicine, Inc. (PRME)

Footnote F1

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.

Footnote F2

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.

Footnote F3

This transaction was entered into pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on April 6, 2023.

Footnote F4

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $14.90 to $15.22, 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 4 and in footnote 6 of this Form 4.

Footnote F5

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.

Footnote F6

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $14.78 to $15.09, inclusive.

Footnote F7

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.