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 OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

1. Name and Address of Reporting Person *

Marshall Keith W		 2. Issuer Name and Ticker or Trading Symbol

Prometheus Biosciences, Inc. [ RXDX ] 		5. Relationship of Reporting Person(s) to Issuer (Check all applicable)

_____ Director                    _____ 10% Owner
__X__ Officer (give title below)    _____ Other (specify below)
Chief Financial Officer
(Last)          (First)          (Middle)

C/O PROMETHEUS BIOSCIENCES, INC., 3050 SCIENCE PARK ROAD		 3. Date of Earliest Transaction (MM/DD/YYYY)

6/16/2023
(Street)

SAN DIEGO, CA 92121		 4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
 6. Individual or Joint/Group Filing (Check Applicable Line)

_X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)        (State)        (Zip)
Rule 10b5-1(c) Transaction Indication
☐ Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. 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 6/16/2023  D  87973 (1)D (2)(3)0 D  

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)		2. Conversion or Exercise Price of Derivative Security3. Trans. Date3A. Deemed Execution Date, if any4. Trans. Code
(Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date7. 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 of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)11. Nature of Indirect Beneficial Ownership (Instr. 4)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock Option (right to buy) $3.10 6/16/2023  D     52838   (2)(3)8/11/2030 Common Stock 52838  (2)(3)0 D  
Stock Option (right to buy) $3.70 6/16/2023  D     93040   (2)(3)12/17/2030 Common Stock 93040  (2)(3)0 D  
Stock Option (right to buy) $6.70 6/16/2023  D     135913   (2)(3)2/3/2031 Common Stock 135913  (2)(3)0 D  
Stock Option (right to buy) $36.32 6/16/2023  D     102155   (2)(3)11/13/2031 Common Stock 102155  (2)(3)0 D  
Stock Option (right to buy) $29.56 6/16/2023  D     86582   (2)(3)5/19/2032 Common Stock 86582  (2)(3)0 D  
Stock Option (right to buy) $110.20 6/16/2023  D     34085   (2)(3)12/8/2032 Common Stock 34085  (2)(3)0 D  
Stock Option (right to buy) $108.76 6/16/2023  D     12920   (2)(3)12/15/2032 Common Stock 12920  (2)(3)0 D  
Explanation of Responses:
(1) Includes 9,811 restricted stock units.
(2) Pursuant to the Agreement and Plan of Merger, dated April 15, 2023, by and among the Issuer, Merck & Co., Inc. ("Merck") and Splash Merger Sub, Inc., the Issuer became a wholly owned subsidiary of Merck upon consummation of the merger (the "Effective Time"). At the Effective Time, (a) each of the Issuer's outstanding shares of common stock was cancelled and automatically converted into the right to receive $200 in cash (the "Merger Consideration"), without interest,... (Continued in Footnote 3)
(3) (Continued from Footnote 2) ...(b) each of the Issuer's outstanding restricted stock units ("RSUs") was automatically cancelled and converted into the right to receive an amount in cash equal to the product of (i) the number of shares of the Issuer's common stock underlying such RSU immediately prior to the Effective Time multiplied by (ii) the Merger Consideration, without interest and (c) each of the Issuer's outstanding unexercised stock options, whether vested or unvested, was automatically cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of (i) the number of shares of the Issuer's common stock underlying such option immediately prior to the Effective Time multiplied by (ii) the amount, if any, by which the Merger Consideration exceeded the exercise price per share of such option.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director10% OwnerOfficerOther
Marshall Keith W
C/O PROMETHEUS BIOSCIENCES, INC.
3050 SCIENCE PARK ROAD
SAN DIEGO, CA 92121

Chief Financial Officer
Signatures
/s/ Keith W. Marshall6/16/2023
**Signature of Reporting PersonDate
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).
**Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note:File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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