UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
SCHEDULE 13G
 
 
Under the Securities Exchange Act of 1934
(Amendment No. 1)*
 
Atara Biotherapeutics, Inc. 
(Name of Issuer)
 
Common Stock
(Title of Class of Securities)
 
046513107
(CUSIP Number)
 
March 31, 2015
(Date of Event Which Requires Filing of this Statement)
 
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
 
     x  Rule 13d-1(b)
 
     o  Rule 13d-1(c)
 
     o  Rule 13d-1(d)
 
* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
 
The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).
 
 
 
 
 
CUSIP No.  046513107      
 
      
1 NAMES OF REPORTING PERSONS
I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
 The Baupost Group, L.L.C.
04-3402144
   
2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)

 (a)   o
 (b)   x
   
3 SEC USE ONLY
  
  
   
4 CITIZENSHIP OR PLACE OF ORGANIZATION
  
 The Commonwealth of Massachusetts
    
NUMBER OF SHARES BENEFICIALLY  OWNED BY EACH REPORTING PERSON WITH: 5 SOLE VOTING POWER
  
 0
   
6 SHARED VOTING POWER
  
 4,763,265
   
7 SOLE DISPOSITIVE POWER
  
 0
   
8 SHARED DISPOSITIVE POWER
  
 4,763,265
   
9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
  
 4,763,265
   
10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
  
 o
   
11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
  
 19.55%
   
12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
  
 IA
 

FOOTNOTES
  
 
 
 
 
 
CUSIP No.  046513107      
 
      
1 NAMES OF REPORTING PERSONS
I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
 SAK Corporation
04-3334541
   
2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)

 (a)   o
 (b)   x
   
3 SEC USE ONLY
  
  
   
4 CITIZENSHIP OR PLACE OF ORGANIZATION
  
 The Commonwealth of Massachusetts
    
NUMBER OF SHARES BENEFICIALLY  OWNED BY EACH REPORTING PERSON WITH: 5 SOLE VOTING POWER
  
 0
   
6 SHARED VOTING POWER
  
 4,763,265
   
7 SOLE DISPOSITIVE POWER
  
 0
   
8 SHARED DISPOSITIVE POWER
  
 4,763,265
   
9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
  
 4,763,265
   
10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
  
 o
   
11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
  
 19.55%
   
12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
  
 HC
 

FOOTNOTES
  
 
 
 
 
 
CUSIP No.  046513107      
 
      
1 NAMES OF REPORTING PERSONS
I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
 Seth A. Klarman
   
2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)

 (a)   o
 (b)   x
   
3 SEC USE ONLY
  
  
   
4 CITIZENSHIP OR PLACE OF ORGANIZATION
  
 The United States of America
    
NUMBER OF SHARES BENEFICIALLY  OWNED BY EACH REPORTING PERSON WITH: 5 SOLE VOTING POWER
  
 0
   
6 SHARED VOTING POWER
  
 4,763,265
   
7 SOLE DISPOSITIVE POWER
  
 0
   
8 SHARED DISPOSITIVE POWER
  
 4,763,265
   
9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
  
 4,763,265
   
10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
  
 o
   
11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
  
 19.55%
   
12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
  
 HC
 

FOOTNOTES
  
 
 
 
 
 
Item 1.

 
(a)
Name of Issuer
 
 
Atara Biotherapeutics, Inc.

 
(b)
Address of Issuer’s Principal Executive Offices
 
 
3260 Bayshore Boulevard
Brisbane, California 94005

Item 2.

 
(a)
Name of Person Filing
 
 
 (1)
The Baupost Group, L.L.C.
 
 
 (2)
SAK Corporation
 
 
 (3)
Seth A. Klarman

 
(b)
Address of Principal Business Office or, if none, Residence
 
 
 (1)
The Baupost Group, L.L.C.
10 St. James Avenue, Suite 1700
Boston, Massachusetts 02116
 
 
 (2)
SAK Corporation
10 St. James Avenue, Suite 1700
Boston, Massachusetts 02116
 
 
 (3)
Seth A. Klarman
10 St. James Avenue, Suite 1700
Boston, Massachusetts 02116

 
(c)
Citizenship
 
 
 (1)
The Baupost Group, L.L.C.: The Commonwealth of Massachusetts
 
 
 (2)
SAK Corporation: The Commonwealth of Massachusetts
 
 
 (3)
Seth A. Klarman: The United States of America

 
(d)
Title of Class of Securities
 
 
Common Stock

 
(e)
CUSIP Number
 
 
046513107

 
Item 3.
If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

 
(a)
o
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

 
(b)
o
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

 
(c)
o
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

 
(d)
o
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

 
(e)
x
An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

 
(f)
o
An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

 
(g)
x
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

 
(h)
o
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

 
(i)
o
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

 
(j)
o
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J).

 
(k)
o
A group, in accordance with § 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:

 
 
 
 
 
Item 4.
Ownership.
 
Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

 
(a)
Amount beneficially owned:
 
 
 (1)
The Baupost Group, L.L.C.: 4,763,265
 
 
 (2)
SAK Corporation: 4,763,265
 
 
 (3)
Seth A. Klarman: 4,763,265

 
(b)
Percent of class:
 
 
 (1)
The Baupost Group, L.L.C.: 19.55%
 
 
 (2)
SAK Corporation: 19.55%
 
 
 (3)
Seth A. Klarman: 19.55%

 
(c)
Number of shares as to which the person has:

 
(i)
Sole power to vote or to direct the vote:
 
 
 
 (1)
The Baupost Group, L.L.C.: 0
 
 
 
 (2)
SAK Corporation: 0
 
 
 
 (3)
Seth A. Klarman: 0

 
(ii)
Shared power to vote or to direct the vote:
 
 
 
 (1)
The Baupost Group, L.L.C.: 4,763,265
 
 
 
 (2)
SAK Corporation: 4,763,265
 
 
 
 (3)
Seth A. Klarman: 4,763,265

 
(iii)
Sole power to dispose or to direct the disposition of:
 
 
 
 (1)
The Baupost Group, L.L.C.: 0
 
 
 
 (2)
SAK Corporation: 0
 
 
 
 (3)
Seth A. Klarman: 0

 
(iv)
Shared power to dispose or to direct the disposition of:
 
 
 
 (1)
The Baupost Group, L.L.C.: 4,763,265
 
 
 
 (2)
SAK Corporation: 4,763,265
 
 
 
 (3)
Seth A. Klarman: 4,763,265

Item 5.
Ownership of Five Percent or Less of a Class
 
If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following o .
 
 
 
Item 6.
Ownership of More than Five Percent on Behalf of Another Person.
 
Securities reported on this statement on Schedule 13G as being beneficially owned by Baupost were purchased on behalf of various private investment limited partnerships.
 
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company
 
See footnote.
 
Item 8.
Identification and Classification of Members of the Group
 
Not applicable.
 
Item 9.
Notice of Dissolution of Group
 
Not applicable.
 
 
 
 
 
 
Item 10.
Certification
  
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under §240.14a-11.
 
 

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
 
 
 The Baupost Group, L.L.C.
 
    
Date: April 09, 2015
By:
/s/  Seth A. Klarman 
   Name: Seth A. Klarman 
   Title:  President 
    
 
 
 
 SAK Corporation
 
    
Date: April 09, 2015
By:
/s/  Seth A. Klarman 
   Name: Seth A. Klarman 
   Title:  President 
    
 
 
 
 Seth A. Klarman
 
    
Date: April 09, 2015
By:
/s/  Seth A. Klarman 
   Name: Seth A. Klarman 
   
    
 
Footnotes:
Item 3, Item 4 and Item 7

This statement on Schedule 13G is being jointly filed by The Baupost Group, L.L.C. ("Baupost"), SAK Corporation and Seth A. Klarman. Baupost is a registered investment adviser and acts as an investment adviser and general partner to certain private investment limited partnerships. SAK Corporation is the Manager of Baupost. Mr. Klarman, as the sole shareholder of SAK Corporation and a controlling person of Baupost, may be deemed to have beneficial ownership under Section 13 of the Securities Exchange Act of 1934, as amended, of the securities beneficially owned by Baupost. Securities reported on this statement on Schedule 13G as being beneficially owned by Baupost were purchased on behalf of various private investment limited partnerships.

Pursuant to Rule 13d-4, Seth A. Klarman and SAK Corporation declare that the filing of this statement on Schedule 13G shall not be deemed an admission by either or both of them that they are, for the purposes of Section 13 of the Securities Exchange Act of 1934, as amended, the beneficial owner of any securities covered by this statement on Schedule 13G.

Attention:
Intentional misstatements or omissions of fact constitute Federal criminal violations (See 18 U.S.C. 1001)