Defects in DNA ligase i trigger PCNA ubiquitylation at Lys 107

Sapna Das-Bradoo, Hai Dang Nguyen, Jamie L. Wood, Robin M. Ricke, Justin C. Haworth, Anja Katrin Bielinsky

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


In all eukaryotes, the ligation of newly synthesized DNA, also known as Okazaki fragments, is catalysed by DNA ligase I (ref. 1). An individual with a DNA ligase I deficiency exhibits growth retardation, sunlight sensitivity and severe immunosuppression, probably due to accumulation of DNA damage. Surprisingly, not much is known about the DNA damage response (DDR) in DNA ligase I-deficient cells. As DNA replication and DDR pathways are highly conserved in eukaryotes, we used Saccharomyces cerevisiae as a model system to address this issue. We uncovered a new pathway, which facilitates ubiquitylation at Lys 107 of proliferating cell nuclear antigen (PCNA). Unlike ubiquitylation at Lys 164 of PCNA in response to UV irradiation, which triggers translesion synthesis, modification of Lys 107 is not dependent on the ubiquitin conjugating enzyme (E2) Rad6 (ref. 4) nor the ubiquitin ligase (E3) Rad18 (ref. 5), but requires the E2 variant Mms2 (ref. 6) in conjunction with Ubc4 (ref. 7) and the E3 Rad5 (Refs 8, 9). Surprisingly, DNA ligase I-deficient S. cerevisiae cdc9-1 cells that carry a PCNAK107R mutation are inviable, because they cannot activate a robust DDR. Furthermore, we show that ubiquitylation of PCNA in response to DNA ligase I deficiency is conserved in humans, yet the lysine residue that is modified remains to be determined. We propose that PCNA ubiquitylation provides a 'DNA damage code' that allows cells to categorize different types of defects that arise during DNA replication.

Original languageEnglish (US)
Pages (from-to)74-79
Number of pages6
JournalNature Cell Biology
Issue number1
StatePublished - Jan 2010

Bibliographical note

Funding Information:
We thank D. J. Clarke, J. F. X. Diffley, D. Durocher, S. J. Elledge, M. Hochstrasser, S. Jentsch, D. Koepp and D. M. Livingston for strains and plasmids and J. F. X. Diffley, A. E. Tomkinson and Z. Zhang for antibodies against Rad53, Cdc9 and PCNA. We acknowledge the assistance of the Flow Cytometry Core Facility at the University of Minnesota. Molecular graphics images were produced using the UCSF Chimera package from the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco (supported by NIH P41 RR‑01081). J.C.H. was supported by NIH training grant CA009138. This work was supported by a Grant‑in‑Aid from the University of Minnesota and NIH grant (GM074917) to A.K.B. who is a Scholar of the Leukemia and Lymphoma Society.


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