Document:

FORM OF STOCK OPTION AGREEMENT

 EXHIBIT 4.2 
  

GENESOFT PHARMACEUTICALS, INC. 
 FORM OF STOCK OPTION AGREEMENT 
  
 RECITALS

  
 A.    The Board has approved the
grant of an option for the purpose of retaining the services of the designated Employee, non-employee member of the Board or the board of directors of any Parent or Subsidiary and consultants or other independent advisor in the service of the
Corporation (or any Parent or Subsidiary). 
  
 B.    Optionee is to render valuable services to the Corporation (or a Parent or Subsidiary), and this Agreement is executed to carry out the purposes of the Corporation in granting an option to Optionee. 
  
 C.    All capitalized terms in this Agreement shall have
the meaning assigned to them in the attached Appendix. 
  
 NOW,
THEREFORE, it is hereby agreed as follows: 
  
 1.    Grant of Option. The Corporation hereby grants to Optionee, as of the Grant Date, an option to purchase up to the number of Option Shares specified in the Grant Notice. The Option Shares shall be
purchasable from time to time during the option term specified in Paragraph 2 at the Exercise Price. 
  
 2.    Option Term. This option shall have a term of ten (10) years measured from the Grant Date and shall accordingly
expire at the close of business on the Expiration Date, unless sooner terminated in accordance with Paragraph 5 or 6. 
  
 3.    Limited Transferability. This option shall be neither transferable nor assignable by Optionee other than by will
or by the laws of descent and distribution following Optionee’s death and may be exercised, during Optionee’s lifetime, only by Optionee. 
  
 4.    Dates of Exercise. This option shall become exercisable for the Option Shares in one or more installments as
specified in the Grant Notice. As the option becomes exercisable for such installments, those installments shall accumulate, and the option shall remain exercisable for the accumulated installments until the Expiration Date or sooner termination of
the option term under Paragraph 5 or 6. 
  
 5.    Cessation of Service. The option term specified in Paragraph 2 shall terminate (and this option shall cease to be outstanding) prior to the Expiration Date should any of the following provisions
become applicable: 

 (a)    Should Optionee cease to remain in Service for any reason
(other than death, Disability or Misconduct) while this option is outstanding, then the period for which this option shall remain exercisable shall be reduced to a three (3)-month period commencing with the date of such cessation of Service, but in
no event shall this option be exercisable at any time after the Expiration Date. 
  
 (b)    Should Optionee die while holding this option, then the personal representative of Optionee’s estate or
the person or persons to whom the option is transferred pursuant to Optionee’s will or in accordance with the laws of inheritance shall have the right to exercise this option. Such right shall lapse, and this option shall cease to be
outstanding, upon the earlier of (i) the expiration of the twelve (12)-month period measured from the date of Optionee’s death or (ii) the Expiration Date. 
  

(c)    Should Optionee cease Service by reason of Disability while this option is outstanding, then the period for
which this option shall remain exercisable shall be reduced to a twelve (12)-month period commencing with the date of such cessation of Service. In no event, however, shall this option be exercisable at any time after the Expiration Date.

  
 (d)    During the limited
period of post-Service exercisability, this option may not be exercised in the aggregate for more than the number of Option Shares in which Optionee is, at the time of Optionee’s cessation of Service, vested pursuant to the Vesting Schedule
specified in the Grant Notice or the special vesting acceleration provisions of Paragraph 6. Upon the expiration of such limited exercise period or (if earlier) upon the Expiration Date, this option shall terminate and cease to be outstanding for
any vested Option Shares for which the option has not been exercised. To the extent Optionee is not vested in the Option Shares at the time of Optionee’s cessation of Service, this option shall immediately terminate and cease to be outstanding
with respect to those shares. 
  
 (e)    Should Optionee’s Service be terminated for Misconduct, then this option shall terminate immediately and cease to remain outstanding. 
  
 6.    Accelerated Vesting. 
  
 (a)    In the event of any Corporate Transaction, the Option Shares at the time subject
to this option but not otherwise vested shall automatically vest in full so that this option shall, immediately prior to the effective date of the Corporate Transaction, become fully exercisable for all of the Option Shares as fully-vested shares
and may be exercised for any or all of those vested shares. However, the Option Shares shall not vest on such an accelerated basis if and to the extent: (i) this option is assumed by the successor corporation (or parent thereof) in the
Corporate Transaction and the Corporation’s repurchase rights with respect to the unvested Option Shares are assigned to such successor corporation (or parent thereof) or (ii) this option is to be replaced with a cash incentive program of the
successor corporation which preserves the spread existing on the unvested Option Shares at the time of the Corporate Transaction (the excess of the Fair Market Value of those Option Shares over the Exercise Price payable for such shares) and
provides for subsequent payout in accordance with the same Vesting Schedule applicable to those unvested Option Shares as set forth in the Grant Notice. 
  

 2 

 (b)    Immediately following the Corporate Transaction, this option
shall terminate and cease to be outstanding, except to the extent assumed by the successor corporation (or parent thereof) in connection with the Corporate Transaction. 
  
 (c)    If this option is assumed in connection with a Corporate Transaction, then this
option shall be appropriately adjusted, immediately after such Corporate Transaction, to apply to the number and class of securities which would have been issuable to Optionee in consummation of such Corporate Transaction had the option been
exercised immediately prior to such Corporate Transaction, and appropriate adjustments shall also be made to the Exercise Price, provided, the aggregate Exercise Price shall remain the same. 
  
 (d)    The Option Shares may also vest
upon an accelerated basis in accordance with the terms and conditions of any special addendum attached to this Agreement. 
  
 (e)    This Agreement shall not in any way affect the right of the Corporation to adjust, reclassify, reorganize or
otherwise change its capital or business structure or to merge, consolidate, dissolve, liquidate or sell or transfer all or any part of its business or assets. 
  

7.    Adjustment in Option Shares. Should any change be made to the Common Stock by reason of any stock split, stock
dividend, recapitalization, combination of shares, exchange of shares or other change affecting the outstanding Common Stock as a class without the Corporation’s receipt of consideration, appropriate adjustments shall be made to (i) the total
number and/or class of securities subject to this option and (ii) the Exercise Price in order to reflect such change and thereby preclude a dilution or enlargement of benefits hereunder. 
  
 8.    Stockholder Rights. The holder of this option shall not have any stockholder rights
with respect to the Option Shares until such person shall have exercised the option, paid the Exercise Price and become the record holder of the purchased shares. 
  
 9.    Manner of Exercising Option. 
  
 (a)    In order to exercise this option
with respect to all or any part of the Option Shares for which this option is at the time exercisable, Optionee (or any other person or persons exercising the option) must take the following actions: 
  
 (i)    Execute and deliver to the
Corporation a Purchase Agreement for the Option Shares for which the option is exercised. 
  
 (ii)    Pay the aggregate Exercise Price for the purchased shares in one or more of the following forms: 

 
 (A)    cash or check made payable to
the Corporation; or 
  
 (B)    a promissory note payable to the Corporation, but only to the extent authorized by the Board in accordance with Paragraph 14. 
  

 3 

 Should the Common Stock be registered under Section 12 of the 1934 Act at the time the
option is exercised, then the Exercise Price may also be paid as follows: 
  
 (C)    in shares of Common Stock held by Optionee (or any other person or persons exercising the option) for the requisite period necessary to avoid a charge to the Corporation’s earnings for
financial reporting purposes and valued at Fair Market Value on the Exercise Date; or 
  
 (D)    to the extent the option is exercised for vested Option Shares, through a special sale and remittance
procedure pursuant to which Optionee (or any other person or persons exercising the option) shall concurrently provide irrevocable instructions (a) to a Corporation designated brokerage firm to effect the immediate sale of the purchased shares and
remit to the Corporation, out of the sale proceeds available on the settlement date, sufficient funds to cover the aggregate Exercise Price payable for the purchased shares plus all applicable Federal, state and local income and employment taxes
required to be withheld by the Corporation by reason of such exercise and (b) to the Corporation to deliver the certificates for the purchased shares directly to such brokerage firm in order to complete the sale. 
  
 Except to the extent the sale and remittance procedure is
utilized in connection with the option exercise, payment of the Exercise Price must accompany the Purchase Agreement delivered to the Corporation in connection with the option exercise. 
  
 (iii)    Furnish to the Corporation appropriate documentation that the person or persons
exercising the option (if other than Optionee) have the right to exercise this option. 
  
 (iv)    Execute and deliver to the Corporation such written representations as may be requested by the Corporation in
order for it to comply with the applicable requirements of Federal and state securities laws. 
  
 (v)    Make appropriate arrangements with the Corporation (or Parent or Subsidiary employing or retaining Optionee)
for the satisfaction of all Federal, state and local income and employment tax withholding requirements applicable to the option exercise. 
  
 (b)    As soon as practical after the Exercise Date, the Corporation shall issue to or on behalf of Optionee (or any
other person or persons exercising this option) a certificate for the purchased Option Shares, with the appropriate legends affixed thereto. 
  
 (c)    In no event may this option be exercised for any fractional shares. 
  

 4 

 10.    REPURCHASE RIGHTS. ALL OPTION SHARES ACQUIRED UPON THE
EXERCISE OF THIS OPTION SHALL BE SUBJECT TO CERTAIN RIGHTS OF THE CORPORATION AND ITS ASSIGNS TO REPURCHASE THOSE SHARES IN ACCORDANCE WITH THE TERMS SPECIFIED IN THE PURCHASE AGREEMENT. 
  
 11.    Compliance with Laws and
Regulations. 
  
 (a)    The exercise of this option and the issuance of the Option Shares upon such exercise shall be subject to compliance by the Corporation and Optionee with all applicable requirements of law relating thereto and with
all applicable regulations of any stock exchange (or the Nasdaq National Market, if applicable) on which the Common Stock may be listed for trading at the time of such exercise and issuance. 
  
 (b)    The inability of the Corporation
to obtain approval from any regulatory body having authority deemed by the Corporation to be necessary to the lawful issuance and sale of any Common Stock pursuant to this option shall relieve the Corporation of any liability with respect to the
non-issuance or sale of the Common Stock as to which such approval shall not have been obtained. The Corporation, however, shall use its best efforts to obtain all such approvals. 
  
 12.    Successors and Assigns. Except to the extent otherwise provided in Paragraphs 3 and
6, the provisions of this Agreement shall inure to the benefit of, and be binding upon, the Corporation and its successors and assigns and Optionee, Optionee’s assigns and the legal representatives, heirs and legatees of Optionee’s estate.

  
 13.    Notices. Any notice
required to be given or delivered to the Corporation under the terms of this Agreement shall be in writing and addressed to the Corporation at its principal corporate offices. Any notice required to be given or delivered to Optionee shall be in
writing and addressed to Optionee at the address indicated below Optionee’s signature line on the Grant Notice. All notices shall be deemed effective upon personal delivery or upon deposit in the U.S. mail, postage prepaid and properly
addressed to the party to be notified. 
  
 14.    Financing. The Board may, in its absolute discretion and without any obligation to do so, permit Optionee to pay the Exercise Price for the purchased Option Shares by delivering a full-recourse,
interest-bearing promissory note secured by those Option Shares. The payment schedule in effect for any such promissory note shall be established by the Board in its sole discretion. 
  
 15.    Construction. This option evidenced hereby is made and granted pursuant to this
Agreement and is in all respects limited by and subject to the terms of this Agreement. All decisions of the Board with respect to any question or issue arising under this Agreement shall be conclusive and binding on all persons having an interest
in this option. 
  
 16.    Governing
Law. The interpretation, performance and enforcement of this Agreement shall be governed by the laws of the State of California without resort to that State’s conflict-of-laws rules. 
  

 5 

 APPENDIX 
  

The following definitions shall be in effect under the Agreement: 
  
 A.    Agreement shall mean this Stock Option Agreement. 
  
 B.    Board shall mean the
Corporation’s Board of Directors. 
  
 C.    Code shall mean the Internal Revenue Code of 1986, as amended. 
  
 D.    Common Stock shall mean the Corporation’s common stock. 
  
 E.    Corporate Transaction shall mean
either of the following stockholder-approved transactions to which the Corporation is a party: 
  
 (i)    a merger or consolidation in which securities possessing more than fifty percent (50%) of the total combined
voting power of the Corporation’s outstanding securities are transferred to a person or persons different from the persons holding those securities immediately prior to such transaction, or 
  
 (ii)    the sale, transfer or other
disposition of all or substantially all of the Corporation’s assets in complete liquidation or dissolution of the Corporation. 
  
 F.    Corporation shall mean GeneSoft Pharmaceuticals, Inc., a Delaware corporation. 
  
 G.    Disability shall mean the inability
of Optionee to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment and shall be determined by the Board on the basis of such medical evidence as the Board deems warranted under the
circumstances. Disability shall be deemed to constitute Permanent Disability in the event that such Disability is expected to result in death or has lasted or can be expected to last for a continuous period of twelve (12) months or more.

  
 H.    Employee shall mean an
individual who is in the employ of the Corporation (or any Parent or Subsidiary), subject to the control and direction of the employer entity as to both the work to be performed and the manner and method of performance. 
  
 I.    Exercise Date shall mean the date on
which the option shall have been exercised in accordance with Paragraph 9 of the Agreement. 
  
 J.    Exercise Price shall mean the exercise price payable per Option Share as specified in the Grant Notice. 
  
 K.    Expiration Date shall mean the date on which the option expires as specified in the
Grant Notice. 
  

 A-1 

 L.    Fair Market Value per share of Common Stock on any relevant date
shall be determined in accordance with the following provisions: 
  
 (i)    If the Common Stock is at the time traded on the Nasdaq National Market, then the Fair Market Value shall be the closing price per share of Common Stock on the date in question, as the price
is reported by the National Association of Securities Dealers on the Nasdaq National Market. If there is no closing price for the Common Stock on the date in question, then the Fair Market Value shall be the closing price on the last preceding date
for which such quotation exists. 
  
 (ii)    If the Common Stock is at the time listed on any Stock Exchange, then the Fair Market Value shall be the closing selling price per share of Common Stock on the date in question on the Stock Exchange determined by
the Board to be the primary market for the Common Stock, as such price is officially quoted in the composite tape of transactions on such exchange. If there is no closing selling price for the Common Stock on the date in question, then the Fair
Market Value shall be the closing selling price on the last preceding date for which such quotation exists. 
  
 (iii)    If the Common Stock is at the time neither listed on any Stock Exchange nor traded on the Nasdaq National
Market, then the Fair Market Value shall be determined by the Board after taking into account such factors as the Board shall deem appropriate. 
  
 M.    Grant Date shall mean the date of grant of the option as specified in the Grant Notice. 
  
 N.    Grant Notice shall mean the Notice of
Grant of Stock Option accompanying the Agreement, pursuant to which Optionee has been informed of the basic terms of the option evidenced hereby. 
  
 O.    Misconduct shall mean the commission of any act of fraud, embezzlement or dishonesty by Optionee, any unauthorized
use or disclosure by Optionee of confidential information or trade secrets of the Corporation (or any Parent or Subsidiary), or any other intentional misconduct by Optionee adversely affecting the business or affairs of the Corporation (or any
Parent or Subsidiary) in a material manner. The foregoing definition shall not be deemed to be inclusive of all the acts or omissions which the Corporation (or any Parent or Subsidiary) may consider as grounds for the dismissal or discharge of
Optionee or any other individual in the Service of the Corporation (or any Parent or Subsidiary). 
  
 P.    1934 Act shall mean the Securities Exchange Act of 1934, as amended. 
  
 Q.    Non-Statutory Option shall mean an
option not intended to satisfy the requirements of Code Section 422. 
  
 R.    Option Shares shall mean the number of shares of Common Stock subject to the option. 
  

 A-2 

 S.    Optionee shall mean the person to whom the option is granted as
specified in the Grant Notice. 
  
 T.    Parent shall mean any corporation (other than the Corporation) in an unbroken chain of corporations ending with the Corporation, provided each corporation in the unbroken chain (other than the
Corporation) owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock in one of the other corporations in such chain. 
  
 U.    Purchase Agreement shall mean the
stock purchase agreement in substantially the form of Exhibit B to the Grant Notice. 
  
 V.    Service shall mean the Optionee’s performance of services for the Corporation (or any Parent or Subsidiary) in the capacity of an Employee, a non-employee member of the
board of directors or an independent consultant. 
  
 W.    Stock Exchange shall mean the American Stock Exchange or the New York Stock Exchange. 
  
 X.    Subsidiary shall mean any corporation (other than the Corporation) in an unbroken chain of corporations beginning
with the Corporation, provided each corporation (other than the last corporation) in the unbroken chain owns, at the time of the determination, stock possessing fifty percent (50%) or more of the total combined voting power of all classes of stock
in one of the other corporations in such chain. 
  
 AB.    Vesting Schedule shall mean the vesting schedule specified in the Grant Notice pursuant to which the Optionee is to vest in the Option Shares in a series of installments over his or her period of
Service. 
  
  

 A-3 

 SCHEDULE 
  
 List of Optionees under the Stock Option Agreement 
  

						
	 Name

	  	Shares (1)

	  	Exercise Price
per Share (2)

	Trevor McCann	  	23,809	  	$	1.68
	Glenn Tillotson	  	23,809	  	$	1.68
	Tom Seldman	  	35,714	  	$	1.68

  

	 	(1)	Represents number of shares of common stock, $0.10 par value per share, of Genome Therapeutics Corp. 

  

	 	(2)	Subject to adjustment. 

  

 A-1FORM OF STOCK OPTION ASSUMPTION AGREEMENT

 Exhibit 4.3 
  

GENOME THERAPEUTICS CORP. 
 STOCK OPTION
ASSUMPTION AGREEMENT 
  
 OPTIONEE: 
  
 STOCK OPTION ASSUMPTION AGREEMENT issued as of the 6th day of February, 2004
by Genome Therapeutics Corp., a Massachusetts corporation (“Genome”). 
  
 WHEREAS,                              (“Optionee”) holds one
or more outstanding options to purchase shares of the common stock of GeneSoft Pharmaceuticals, Inc., a Delaware corporation (“GeneSoft”), which were granted to Optionee under GeneSoft’s 1998 Stock Option/Stock Issuance Plan (as
amended and restated from time to time, the “Plan”), and are evidenced by a Stock Option Agreement (the “Option Agreement”) between GeneSoft and Optionee. 
  
 WHEREAS, GeneSoft has been acquired as of February 6, 2004 by Genome through merger of a wholly owned Genome subsidiary,
Guardian Acquisition, Inc (“Merger Sub”), with and into GeneSoft (the “Merger”) pursuant to the Agreement and Plan of Merger and Reorganization dated as of November 17, 2003 by and among Genome, GeneSoft, Merger Sub and Luke
Evnin, as Stockholders’ Representative (the “Merger Agreement”). 
  
 WHEREAS, the provisions of the Merger Agreement require Genome to assume all obligations of GeneSoft under all options outstanding under the Plan upon the consummation of the Merger (the “GeneSoft Options”).

  
 WHEREAS, pursuant to the provisions of the Merger Agreement,
Optionee’s GeneSoft Options now represent options (“Genome Options”) to purchase shares of Genome Common Stock, $0.10 par value, (“Genome Stock”). 
  
 WHEREAS, the number of shares of Genome Stock which are subject to Optionee’s Genome Options is equal to the number of
shares of GeneSoft common stock subject to the unexercised portion of such Genome Option immediately prior to the consummation of the Merger multiplied by the exchange ratio of 1.1905 (the “Common Exchange Ratio”), rounded down to the
nearest whole number, at an exercise price per share equal to the exercise price per share of such GeneSoft Option in effect immediately prior to the consummation of the Merger (the “Effective Time) divided by the Common Exchange Ratio, rounded
up to the nearest whole cent. 
  
 NOW, THEREFORE, it is hereby
agreed as follows: 
  
 1. The number of shares of GeneSoft common
stock subject to the GeneSoft Options held by Optionee under the Plan immediately prior to the Effective Time and the exercise price 

 payable per share are set forth in Exhibit A hereto. Genome hereby assumes, as of the Effective Time, all the
duties and obligations of GeneSoft under each of the GeneSoft Options. In connection with such assumption, the number of shares of Genome Stock purchasable under each GeneSoft Option hereby assumed and the exercise price payable thereunder have been
adjusted to reflect the Common Exchange Ratio at which shares of GeneSoft common stock purchasable under Optionee’s GeneSoft Options were converted into shares of Genome Stock purchasable under Optionee’s Genome Options upon consummation
of the Merger. Accordingly, the number of shares of Genome Stock subject to each GeneSoft Option hereby assumed, and the adjusted exercise price payable per share of Genome Stock under the assumed GeneSoft Option, are indicated for that option in
attached Exhibit B. 
  
 2. It is intended that this Stock
Option Assumption Agreement, including, without limitation, the adjustment provisions of Section 1 above, comply with Section 424(a) of the Internal Revenue Code of 1986, as amended (the “Code”). 
  
 3. The following provisions shall govern each GeneSoft Option hereby assumed
by Genome: 
  
 (a)    The grant date and the
expiration date of each assumed GeneSoft Option and all other provisions which govern either the exercisability or the termination of the assumed GeneSoft Option shall, subject to the following provisions of this Section 3, remain the same as set
forth in the Option Agreement applicable to that option and shall accordingly govern and control Optionee’s rights under this Agreement to purchase Genome Stock. 
  
 (b)    Unless the context otherwise requires, all references to the “Company” in each Option
Agreement and in the Plan (as incorporated into such Option Agreement) shall mean Genome, all references to “Common Stock” shall mean shares of Genome Stock, as the case may be, and all references to the “Board” shall mean the
Board of Directors of Genome. 
  
 (c)    Each
Genome Option shall remain exercisable in accordance with the same installment exercise schedule in effect under the applicable Option Agreement to which such Genome Option relates immediately prior to the Effective Time (subject to any applicable
acceleration provisions set forth therein), with the number of shares of Genome Stock subject to each such installment adjusted to reflect the Common Exchange Rate. The grant date for each assumed GeneSoft Option shall accordingly remain the same as
in effect under the applicable Option Agreement immediately prior to the Merger. 
  
 (d)    For purposes of applying any and all provisions of the Option Agreement relating to Optionee’s status as an employee or other service provider with the Company, Optionee shall be deemed
to continue in such status for so long as Optionee renders services as an employee or otherwise, as the case may be, to Genome or any Genome subsidiary, including (without limitation) GeneSoft, provided however, that if the entity for which Optionee
renders services as an employee or other service provider ceases to be a subsidiary of Genome, Optionee’s status as an employee or other service provider will be deemed terminated at the time that such entity ceases to be a subsidiary of
Genome. Accordingly, the provisions of the Option Agreement 

 governing the termination of the assumed GeneSoft Option upon the Optionee’s cessation of employee or other service
provider status with GeneSoft shall hereafter be applied on the basis of the Optionee’s cessation of employee or other service provider status with Genome and its subsidiaries, and each assumed GeneSoft Option shall accordingly terminate,
within the designated time period in effect under the Option Agreement for that option, following such cessation of employment or service relationship with Genome and its subsidiaries. 
  
 (e)    The adjusted exercise price payable for the Genome Stock subject to each assumed GeneSoft Option
shall be payable in any of the forms authorized under the Option Agreement applicable to that option. For purposes of determining the holding period of any shares of Genome Stock delivered in payment of such adjusted exercise price, the period for
which such shares were held as GeneSoft common stock prior to the Merger shall be taken into account. 
  
 (f)    If Optionee exercises any assumed Genome Option with respect to shares of Genome Stock prior to the Final Resolution Date (as
defined in the Escrow Agreement referred to below), the stock certificates evidencing twenty percent (20%) (20% less the First Release Percentage (as defined in the Escrow Agreement) in the case of an option exercised on or following the
First Release Date (as defined in the Escrow Agreement)) of the Genome Stock purchased upon such exercise shall be delivered to Var & Co., as nominee of U.S Bank National Association (the “Escrow Agent”) and held in escrow pursuant to
the terms of that certain Escrow Agreement dated as of February 6, 2004 (the “Escrow Agreement”) by and among Genome, the Escrow Agent, and Luke Evnin, as representative of the stockholders of GeneSoft, and such shares of Genome Stock
shall be deemed to be Indemnity Escrow Shares (as defined in the Escrow Agreement), and subject to the provisions of the Escrow Agreement. In addition to the foregoing, in the event of any exercise of the Genome Options prior to the Employment
Escrow Release Date (as defined in the Escrow Agreement), 1.96% of the shares of Genome Stock otherwise issuable in connection with such exercise shall be delivered to the Escrow Agent and held in escrow pursuant to the terms of, and subject to the
provisions of, the Escrow Agreement, and such shares of Genome Stock shall be deemed to be Employment Escrow Shares (as defined in the Escrow Agreement). 
  

3. Except to the extent specifically modified by this Stock Option Assumption Agreement, all of the terms and conditions of each Option Agreement as in
effect immediately prior to the Merger shall continue in full force and effect and shall not in any way be amended, revised or otherwise affected by this Stock Option Assumption Agreement. 
  
 IN WITNESS WHEREOF, Genome Therapeutics, Corp. has caused this Stock Option
Assumption Agreement to be executed on its behalf by its duly-authorized officer as of the      day of February, 2004. 
  

			
	GENOME THERAPEUTICS CORP.
		
	By:	 	  

	 	 	 

  

 EXHIBIT A 
  
 Optionee’s Outstanding Options to Purchase Shares of GeneSoft Pharmaceuticals, Inc. 
 Common Stock (Pre-Merger) 
  

 EXHIBIT B 
  
 Optionee’s Outstanding Options to Purchase Shares of Genome Therapeutics, Corp. 
 Common Stock (Post-Merger)

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