SCHEDULE 13G

SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, DC 20549


Under the Securities Exchange Act of 1934
(Amendment No. 1)*

Cerus Corporation

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

*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 disclosures provided in a prior cover page.

The information required on 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 (the “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.  157085101

CUSIP No.  157085101

CUSIP No.  157085101

CUSIP No.  157085101

Amendment No. 1 to Schedule 13G

This Amendment No. 1 to Schedule 13G amends and supplements the previously filed Schedule 13G filed by Julian C. Baker, Felix J. Baker and Baker Bros. Advisors, LLC. Except as supplemented herein, such statements, as heretofore amended and supplemented, remain in full force and effect.

On July 1, 2013, a Certificate of Conversion was filed with the State of Delaware to convert Baker Bros. Advisors, LLC from a limited liability company into a limited partnership named Baker Bros. Advisors LP (the “Adviser”). Baker Bros. Advisors (GP) LLC (the “Adviser GP”) is the sole general partner of the Adviser. This Schedule 13G is being filed jointly by the Adviser, the Adviser GP, Felix J. Baker and Julian C. Baker (collectively, the “Reporting Persons”).

The business address of each of the Reporting Persons is:

c/o Baker Bros. Advisors LP

667 Madison Avenue, 21^st Floor

New York, NY 10065

(212) 339-5633

The Adviser is a limited partnership organized under the laws of the State of Delaware. The Adviser GP is a limited liability company organized under the laws of the State of Delaware. The citizenship of each of Julian C. Baker and Felix J. Baker is the United States of America.

(a) o Broker or dealer registered under Section 15 of the Exchange Act.

(b) o Bank as defined in section 3(a)(6) of the Exchange Act.

(c) o Insurance company as defined in section 3(a)(19) of the Exchange Act.

(d) o Investment company registered under section 8 of the Investment Company Act of 1940.

(e) x An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E).

(f) o An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F).

(g) x A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G).

(h) o A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act.

(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.

(j) o Group, in accordance with Rule 13d-1(b)(1)(ii)(J).

Items 5 through 9 and 11 of each of the cover pages to this Amendment No. 1 are incorporated herein reference. Certain securities of the Issuer are directly held by each of Baker Brothers Life Sciences, L.P. (“Life Sciences”), 14159, L.P. (“14159”), and 667, L.P. (“667”, and together with Life Sciences and 14159, the “Funds”).

Pursuant to the amended and restated management agreements, as amended, among the Adviser, the Funds and their respective general partners, the Adviser has complete and unlimited discretion and authority with respect to the Funds’ investments and voting power over investments.

The Adviser GP, Felix J. Baker and Julian C. Baker as principals of the Adviser GP, and the Adviser may be deemed to be beneficial owners of securities of the Issuer directly held by the Funds, and may be deemed to have the power to vote or direct the vote of and the power to dispose or direct the disposition of such securities.

The Reporting Persons disclaim beneficial ownership of the securities held by each of the Funds, and this Schedule 13G shall not be deemed an admission that the Reporting Persons are the beneficial owners of such securities for purposes of Section 13(d) or for any other purpose.

The information in Item 4 is incorporated herein by reference.

The information in Item 4 is incorporated herein by reference.

N/A

N/A

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.

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.

August 12, 2013