Sec Form 4 Filing - Alta Partners VIII, L.P. @ SUTRO BIOPHARMA INC - 2018-10-01

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 Alta Partners VIII, L.P. 2. Issuer Name and Ticker or Trading Symbol SUTRO BIOPHARMA INC [ STRO] 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) ONE EMBARCADERO CENTER, SUITE 3700 3. Date of Earliest Transaction (MM/DD/YY) 10/01/2018 (Street) SAN FRANCISCO, CA94111 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 10/01/2018 C 589,661 A 589,661 D ( 2 ) Common Stock 10/01/2018 C 458,331 A 1,047,992 D ( 2 ) Common Stock 10/01/2018 C 382,698 A 1,430,690 D ( 2 ) Common Stock 10/01/2018 C 514,211 A 1,944,901 D ( 2 )

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 B Preferred Stock ( 1 ) 10/01/2018 C 10,201,769 ( 1 ) ( 1 ) Common Stock 589,661 $ 0 0 D ( 2 ) Series C Preferred Stock ( 3 ) 10/01/2018 C 12,387,324 ( 3 ) ( 3 ) Common Stock 458,331 $ 0 0 D ( 2 ) Series D Preferred Stock ( 4 ) 10/01/2018 C 9,449,318 ( 4 ) ( 4 ) Common Stock 382,698 $ 0 0 D ( 2 ) Series E Preferred Stock ( 5 ) 10/01/2018 C 18,698,578 ( 5 ) ( 5 ) Common Stock 514,211 $ 0 0 D ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Alta Partners VIII, L.P. ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO, CA94111 X Alta Partners Management VIII, LLC ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO, CA94111 X CHAMPSI FARAH ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO, CA94111 X JANNEY DANIEL ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO, CA94111 X X NOHRA GUY P ONE EMBARCADERO CENTER, SUITE 3700 SAN FRANCISCO, CA94111 X Signatures /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC, the general partner of Alta Partners VIII, L.P. 10/01/2018 Signature of Reporting Person Date /s/ Daniel Janney as Managing Director of Alta Partners Management VIII, LLC 10/01/2018 Signature of Reporting Person Date /s/ Farah Champsi 10/01/2018 Signature of Reporting Person Date /s/ Daniel Janney 10/01/2018 Signature of Reporting Person Date /s/ Guy Nohra 10/01/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of the issuer's Series B Preferred Stock automatically converted into 0.0578 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its firm commitment initial public offering (the "IPO") pursuant to a registration statement on Form S-1 (File No. 333-227103) under the Securities Act of 1933, as amended (the "Registration Statement"), and had no expiration date. ( 2 )The shares directly held by Alta Partners VIII, L.P. ("Alta VIII") are indirectly held by Alta Partners Management VIII, LLC ("Alta Management VIII"), which is the general partner of Alta VIII. The individual managing directors of Alta Management VIII are Farah Champsi, Guy Nohra and Daniel Janney. The managing directors of Alta Management VIII exercise sole voting and investment control with respect to the shares held by Alta VIII. The individual managing directors of Alta Management VIII disclaim beneficial ownership of all shares held by Alta VIII, except to the extent of their pecuniary interests therein. ( 3 )Each share of the issuer's Series C Preferred Stock automatically converted into 0.0370 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. ( 4 )Each share of the issuer's Series D Preferred Stock automatically converted into 0.0405 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date. ( 5 )Each share of the issuer's Series E Preferred Stock automatically converted into 0.0275 share of the issuer's Common Stock on October 1, 2018 in connection with the closing of the issuer's sale of its Common Stock in its IPO pursuant to the Registration Statement, and had no expiration date.

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