title: Defects in DNA ligase I trigger PCNA ubiquitylation at Lys 107.
abstract: 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.
authors.affiliation: University of Minnesota, Department of Biochemistry, Molecular Biology and Biophysics, Minneapolis, MN 55455, USA.
authors.forename: Sapna
authors.initials: S
authors.lastname: Das-Bradoo
authors.forename: Hai Dang
authors.initials: HD
authors.lastname: Nguyen
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Wood
authors.forename: Robin M
authors.initials: RM
authors.lastname: Ricke
authors.forename: Justin C
authors.initials: JC
authors.lastname: Haworth
authors.forename: Anja-Katrin
authors.initials: AK
authors.lastname: Bielinsky
mesh_terms: D001859:Bone Neoplasms / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics* / Q000528:radiation effects; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D012516:Osteosarcoma / Q000235:genetics / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000235:genetics / Q000378:metabolism*; D016196:S Phase / Q000502:physiology / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination
chemical_list: C000607890:CDC9 protein, S cerevisiae; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C000607892:LIG1 protein, human; C112520:MMS2 protein, S cerevisiae; D018809:Proliferating Cell Nuclear Antigen; C063607:RAD18 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C471606:RAD6 protein, S cerevisiae; C501306:Ubc4 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C076225:RAD5 protein, S cerevisiae; D004265:DNA Helicases; D011088:DNA Ligases; D000072481:DNA Ligase ATP; D008239:Lysine