Third Amendment to the Rights Agreement



 Exhibit 4.3 
  
 THIRD AMENDMENT 
 TO THE 
 RIGHTS AGREEMENT 
  
 This Third Amendment, dated as of October 18, 2004 (this “Third Amendment”), amends the Rights Agreement, dated as of March 16, 2001, by
and between ACLARA BioSciences, Inc., a Delaware corporation (the “Company”), and Mellon Investor Services LLC, a New Jersey limited liability company, as rights agent (the “Rights Agent”), as amended by the
Amendment to the Rights Agreement dated as of May 28, 2004 (the “First Amendment”) and by the Second Amendment to the Rights Agreement dated as of June 11, 2004 (the “Second Amendment”) (as amended by the First
Amendment and by the Second Amendment, the “Rights Agreement”). 
  
 WITNESSETH 
  
 WHEREAS, the Company and the Rights Agent have heretofore executed and entered into the Rights Agreement; 
  
 WHEREAS, pursuant to Section 26 of the Rights Agreement, the Company and the Rights Agent may from time to time supplement or amend the Rights
Agreement in accordance with the provisions of Section 26 thereof; and 
  
 WHEREAS, the Board of Directors of the Company has determined that it is in the best interests of the Company and the holders of the Rights to amend the Rights Agreement as provided herein. 
  
 NOW THEREFORE, in consideration of the foregoing and the mutual
agreements set forth herein, the Company and the Rights Agent agree as follows: 
  
 1. Any term not defined herein shall have the meaning ascribed to it in the Rights Agreement. 
  
 2. Section 1.1 of the Rights Agreement shall be amended and restated in its entirety as follows: 
  
 “1.1 “Acquiring Person” shall mean any Person (as such term
is hereinafter defined) who or which, together with all Affiliates and Associates (as such terms are hereinafter defined) of such Person, shall be the Beneficial Owner (as such term is hereinafter defined) of 20% or more of the Common Shares of the
Company then outstanding but shall not include (i) an Exempt Person (as such term is hereinafter defined), (ii) if, as of the date hereof, any Person is the Beneficial Owner of 20% or more of the Common Shares outstanding (an “Existing
Holder”), such Existing Holder shall not be or become an “Acquiring Person” unless and until such time as such Existing Holder shall become the Beneficial Owner of one or more additional Common Shares of the 







 Company (other than pursuant to a dividend or distribution paid or made by the Company on the
outstanding Common Shares in Common Shares or pursuant to a split or subdivision of the outstanding Common Shares), unless, upon becoming the Beneficial Owner of such additional Common Shares, such Existing Holder is not then the Beneficial Owner of
20% or more of the Common Shares then outstanding, (iii) ViroLogic, Inc., a Delaware corporation (“Parent”), Apollo Acquisition Sub, Inc., a Delaware corporation (“Merger Sub I”), Apollo Merger Subsidiary, LLC, a Delaware limited
liability company (“Merger Sub II,” and together with Merger Sub I, the “Merger Subs”), or any Affiliate or Associate of Parent or the Merger Subs; provided, however, that Parent, the Merger Subs or any Affiliate or
Associate of Parent or the Merger Subs will become an “Acquiring Person” in the event that Parent, the Merger Subs or any Affiliate or Associate of Parent or the Merger Subs becomes the Beneficial Owner, individually or in the aggregate,
of an aggregate of 20% or more of the Common Shares of the Company then outstanding other than pursuant to the terms of the Agreement and Plan of Merger and Reorganization dated as of May 28, 2004 (as it may have been or may be amended from time to
time, the “Merger Agreement”), among the Company, Parent and the Merger Subs or (iv) Perry Corp., a New York corporation, Richard C. Perry, an American citizen, or any Affiliate or Associate of Perry Corp. or Richard C. Perry; provided,
however, that Perry Corp., Richard C. Perry or any Affiliate or Associate of Perry Corp. or Richard C. Perry shall become an “Acquiring Person” in the event that Perry Corp., Richard C. Perry or any Affiliate or Associate of Perry
Corp. or Richard C. Perry becomes the Beneficial Owner, individually or in the aggregate, of an aggregate of 25% or more of the Common Shares of the Company then outstanding. Notwithstanding the foregoing, no Person shall become an “Acquiring
Person” as the result of an acquisition of Common Shares by the Company which, by reducing the number of shares outstanding, increases the proportionate number of shares beneficially owned by such Person to 20% or more (or, in the case of Perry
Corp., Richard C. Perry or any Affiliate or Associate of Perry Corp. or Richard C. Perry, 25% or more, individually or in the aggregate) of the Common Shares of the Company then outstanding; provided, however, that if a Person shall become
the Beneficial Owner of 20% or more (or, in the case of Perry Corp., Richard C. Perry or any Affiliate or Associate of Perry Corp. or Richard C. Perry, 25% or more, individually or in the aggregate) of the Common Shares of the Company then
outstanding solely by reason of share purchases by the Company and shall, after such share purchases by the Company, become the Beneficial Owner of 
  

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 one or more additional Common Shares of the Company (other than pursuant to a dividend or distribution
paid or made by the Company on the outstanding Common Shares in Common Shares or pursuant to a split or subdivision of the outstanding Common Shares), then such Person shall be deemed to be an “Acquiring Person” unless upon becoming the
Beneficial Owner of such additional shares of Common Stock such Person does not beneficially own 20% or more (or, in the case of Perry Corp., Richard C. Perry or any Affiliate or Associate of Perry Corp. or Richard C. Perry, 25% or more,
individually or in the aggregate) of the shares of Common Stock then outstanding. Notwithstanding the foregoing, if the Board of Directors of the Company determines in good faith that a Person who would otherwise be an “Acquiring Person,”
as defined pursuant to the foregoing provisions of this Section 1.1, has become such inadvertently (including, without limitation, because (A) such Person was unaware that it beneficially owned a percentage of Common Stock that would otherwise cause
such Person to be an “Acquiring Person” or (B) such Person was aware of the extent of its Beneficial Ownership of Common Stock but had no actual knowledge of the consequences of such Beneficial Ownership under this Agreement), and without
any intention of changing or influencing control of the Company, and such Person divests as promptly as practicable a sufficient number of Common Shares so that such Person would no longer be an Acquiring Person, as defined pursuant to the foregoing
provisions of this Section 1.1, then such Person shall not be deemed to be or have become an “Acquiring Person” at any time for any purposes of this Agreement. For all purposes of this Agreement, any calculation of the number of Common
Shares outstanding at any particular time, including for purposes of determining the particular percentage of such outstanding Common Shares of which any Person is the Beneficial Owner, shall be made in accordance with the last sentence of Rule
13d-3(d)(1)(i) of the General Rules and Regulations under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), as in effect on the date of this Agreement.” 
  
 3. The first sentence of Section 3.1 of the Rights Agreement shall be amended as follows: 
  
 “Until the earlier of the close of business on (i) the tenth day after
the Shares Acquisition Date or (ii) the tenth Business Day after the date of the commencement of, or first public announcement of the intent of any Person (other than an Exempt Person) to commence, a tender or exchange offer the consummation of
which would result in any Person (other than an Exempt Person) becoming the 
  

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 Beneficial Owner of Common Shares aggregating 20% or more (or, in the case of Perry Corp., Richard C.
Perry or any Affiliate or Associate of Perry Corp. or Richard C. Perry, 25% or more, individually or in the aggregate) of the then outstanding Common Shares of the Company (the earlier of (i) and (ii) being herein referred to as the
“Distribution Date”), (x) the Rights (unless earlier expired, redeemed or terminated) will be evidenced (subject to the provisions of Section 3.2) by the certificates for Common Shares registered in the names of the holders thereof (which
certificates for Common Shares shall also be deemed to be Right Certificates) and not by separate certificates, and (y) the Rights (and the right to receive certificates therefor) will be transferable only in connection with the transfer of the
underlying Common Shares.” 
  
 4. This Third Amendment shall
be deemed to be a contract made under the laws of the State of Delaware and for all purposes shall be governed by and construed in accordance with the laws of such State applicable to contracts to be made and performed entirely within such State;
provided, however, that all provisions regarding the rights, duties and obligations of the Rights Agent shall be governed by and construed in accordance with the laws of the State of New York applicable to contracts made and to be performed
entirely within such State. 
  
 5. This Third Amendment may be
executed in any number of counterparts and each of such counterparts shall for all purposes be deemed to be an original, and all such counterparts shall together constitute but one and the same instrument. 
  
 6. Except as expressly amended hereby, the Rights Agreement shall remain in
full force and effect. 
  
 7. The undersigned officer of the
Company, does hereby certify to the Rights Agent that this Third Amendment (i) complies with the terms of Section 26 of the Rights Agreement and (ii) will not change or increase the rights, duties, liabilities or obligations of the Rights Agent
under the Rights Agreement. 
  

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 IN WITNESS WHEREOF, the parties hereto have caused this Third Amendment to be duly executed as of the day
and year first above written. 
  

			
	ACLARA BIOSCIENCES, INC.,
	a Delaware corporation
		
	By:	 	 /s/ Alfred G. Merriweather


	Name:	 	Alfred Merriweather
	Title:	 	Chief Financial Officer
	
	 MELLON INVESTOR SERVICES LLC,
 as Rights
Agent

		
	By:	 	 /s/ Cecil D. Bobey


	Name:	 	Cecil D. Bobey
	Title:	 	Assistant Vice President