title: Identification of a novel streptococcal gene cassette mediating SOS mutagenesis in Streptococcus uberis.
abstract: Streptococci have been considered to lack the classical SOS response, defined by increased mutation after UV exposure and regulation by LexA. Here we report the identification of a potential self-regulated SOS mutagenesis gene cassette in the Streptococcaceae family. Exposure to UV light was found to increase mutations to antibiotic resistance in Streptococcus uberis cultures. The mutational spectra revealed mainly G:C-->A:T transitions, and Northern analyses demonstrated increased expression of a Y-family DNA polymerase resembling UmuC under DNA-damaging conditions. In the absence of the Y-family polymerase, S. uberis cells were sensitive to UV light and to mitomycin C. Furthermore, the UV-induced mutagenesis was almost completely abolished in cells deficient in the Y-family polymerase. The gene encoding the Y-family polymerase was localized in a four-gene operon including two hypothetical genes and a gene encoding a HdiR homolog. Electrophoretic mobility shift assays demonstrated that S. uberis HdiR binds specifically to an inverted repeat sequence in the promoter region of the four-gene operon. Database searches revealed conservation of the gene cassette in several Streptococcus species, including at least one genome each of Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus thermophilus strains. In addition, the umuC operon was localized in several mobile DNA elements of Streptococcus and Lactococcus species. We conclude that the hdiR-umuC-ORF3-ORF4 operon represents a novel gene cassette capable of mediating SOS mutagenesis among members of the Streptococcaceae.
authors.affiliation: University of Helsinki, Department of Basic Veterinary Sciences, P.O. Box 66, FIN-00014, Finland.
authors.forename: Emilia
authors.initials: E
authors.lastname: Varhimo
authors.forename: Kirsi
authors.initials: K
authors.lastname: Savijoki
authors.forename: Jari
authors.initials: J
authors.lastname: Jalava
authors.forename: Oscar P
authors.initials: OP
authors.lastname: Kuipers
authors.forename: Pekka
authors.initials: P
authors.lastname: Varmanen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015152:Blotting, Northern; D002939:Ciprofloxacin / Q000494:pharmacology; D004249:DNA Damage; D024881:Drug Resistance, Bacterial / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000528:radiation effects; D005798:Genes, Bacterial; D016685:Mitomycin / Q000494:pharmacology; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D009876:Operon; D012293:Rifampin / Q000494:pharmacology; D013014:SOS Response, Genetics / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D012689:Sequence Homology, Nucleic Acid; D013291:Streptococcus / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D001426:Bacterial Proteins; D016685:Mitomycin; D002939:Ciprofloxacin; D012293:Rifampin