SEC Form 4

FORM 4		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 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* Atlas Venture Opportunity Fund II, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Day One Biopharmaceuticals, Inc. [ DAWN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 06/17/2022
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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	06/17/2022		P		766,667	A	$15	766,667	D(1)
Common Stock								7,210,242	I	See footnote(2)
Common Stock								15,714	I	See footnote(3)
Common Stock								991,396	I	See footnote(4)

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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (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: 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

1. Name and Address of Reporting Person* Atlas Venture Opportunity Fund II, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Fund XI, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Associates XI, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Associates XI, LLC (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Opportunity Fund I, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Associates Opportunity I, L.P. (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Atlas Venture Associates Opportunity I, LLC (Last) (First) (Middle) 300 TECHNOLOGY SQUARE, 8TH FLOOR (Street) CAMBRIDGE MA 02139 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. The shares are held directly by Atlas Venture Opportunity Fund II, L.P. ("AVOF II"). The general partner of AVOF II is Atlas Venture Associates Opportunity II, L.P. ("AVAO II LP"). Atlas Venture Associates Opportunity II, LLC ("AVAO II LLC") is the general partner of AVAO II LP. Each of AVAO II LP and AVAO II LLC disclaims Section 16 beneficial ownership of the securities held by AVOF II, except to the extent of its pecuniary interest therein, if any.

2. The shares are held directly by Atlas Venture Fund XI, L.P. ("Atlas Venture Fund XI"). The general partner of Atlas Venture Fund XI is Atlas Venture Associates XI, L.P. ("AVA XI LP"). Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. Each of AVA XI LP and AVA XI LLC disclaims Section 16 beneficial ownership of the securities held by Atlas Venture Fund XI, except to the extent of its pecuniary interest therein, if any.

3. The shares are held directly by AVA XI LP. AVA XI LLC is the general partner of AVA XI LP. AVA XI LLC disclaims Section 16 beneficial ownership of the securities held by AVA XI LP, except to the extent of its pecuniary interest therein, if any.

4. The shares are held directly by Atlas Venture Opportunity Fund I, L.P. ("AVOF I"). The general partner of AVOF I is Atlas Venture Associates Opportunity I, L.P. ("AVAO I LP"). Atlas Venture Associates Opportunity I, LLC ("AVAO I LLC") is the general partner of AVAO I LP. Each of AVAO I LP and AVAO I LLC disclaims Section 16 beneficial ownership of the securities held by AVOF I, except to the extent of its pecuniary interest therein, if any.

Remarks:

	Atlas Venture Opportunity Fund II, L.P., By: Atlas Venture Associates Opportunity II, L.P., By: Atlas Venture Associates Opportunity II, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/22/2022
	Atlas Venture Fund XI, L.P., By: Atlas Venture Associates XI, L.P., its general partner, By: Atlas Venture Associates XI, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan	06/22/2022
	Atlas Venture Associates XI, L.P., By: Atlas Venture Associates XI, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan	06/22/2022
	Atlas Venture Associates XI, LLC By: Ommer Chohan, Chief Financial Officer /s/ Ommer Chohan	06/22/2022
	Atlas Venture Opportunity Fund I, L.P., By: Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/22/2022
	Atlas Venture Associates Opportunity I, L.P., By: Atlas Venture Associates Opportunity I, LLC, its general partner, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/22/2022
	Atlas Venture Associates Opportunity I, LLC, By: Ommer Chohan, Chief Financial Officer, /s/ Ommer Chohan	06/22/2022
	** Signature of Reporting Person	Date
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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