title: (5'S)-8,5'-cyclo-2'-deoxyguanosine is a strong block to replication, a potent pol V-dependent mutagenic lesion, and is inefficiently repaired in Escherichia coli.
abstract: 8,5'-Cyclopurines, making up an important class of ionizing radiation-induced tandem DNA damage, are repaired only by nucleotide excision repair (NER). They accumulate in NER-impaired cells, as in Cockayne syndrome group B and certain Xeroderma Pigmentosum patients. A plasmid containing (5'S)-8,5'-cyclo-2'-deoxyguanosine (S-cdG) was replicated in Escherichia coli with specific DNA polymerase knockouts. Viability was <1% in the wild-type strain, which increased to 5.5% with SOS. Viability decreased further in a pol II(-) strain, whereas it increased considerably in a pol IV(-) strain. Remarkably, no progeny was recovered from a pol V(-) strain, indicating that pol V is absolutely required for bypassing S-cdG. Progeny analyses indicated that S-cdG is significantly mutagenic, inducing ~34% mutation with SOS. Most mutations were S-cdG → A mutations, though S-cdG → T mutation and deletion of 5'C also occurred. Incisions of purified UvrABC nuclease on S-cdG, S-cdA, and C8-dG-AP on a duplex 51-mer showed that the incision rates are C8-dG-AP > S-cdA > S-cdG. In summary, S-cdG is a major block to DNA replication, highly mutagenic, and repaired slowly in E. coli.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, United States.
authors.forename: Vijay P
authors.initials: VP
authors.lastname: Jasti
authors.forename: Rajat S
authors.initials: RS
authors.lastname: Das
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Hilton
authors.forename: Savithri
authors.initials: S
authors.lastname: Weerasooriya
authors.forename: Yue
authors.initials: Y
authors.lastname: Zou
authors.forename: Ashis K
authors.initials: AK
authors.lastname: Basu
mesh_terms: D004260:DNA Repair / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D004261:DNA Replication / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics*; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics / Q000633:toxicity; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D016296:Mutagenesis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D013014:SOS Response, Genetics / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects
chemical_list: C050888:8,5'-cyclo-2'-deoxyguanosine; D012321:DNA-Directed RNA Polymerases; D003849:Deoxyguanosine