title: Contribution of RecFOR machinery of homologous recombination to cell survival after loss of a restriction-modification gene complex.
abstract: Loss of a type II restriction-modification (RM) gene complex, such as EcoRI, from a bacterial cell leads to death of its descendent cells through attack by residual restriction enzymes on undermethylated target sites of newly synthesized chromosomes. Through such post-segregational host killing, these gene complexes impose their maintenance on their host cells. This finding led to the rediscovery of type II RM systems as selfish mobile elements. The host prokaryote cells were found to cope with such attacks through a variety of means. The RecBCD pathway of homologous recombination in Escherichia coli repairs the lethal lesions on the chromosome, whilst it destroys restricted non-self DNA. recBCD homologues, however, appear very limited in distribution among bacterial genomes, whereas homologues of the RecFOR proteins, responsible for another pathway, are widespread in eubacteria, just like the RM systems. In the present work, therefore, we examined the possible contribution of the RecFOR pathway to cell survival after loss of an RM gene complex. A recF mutation reduced survival in an otherwise rec-positive background and, more severely, in a recBC sbcBC background. We also found that its effect is prominent in the presence of specific non-null mutant forms of the RecBCD enzyme: the resistance to killing seen with recC1002, recC1004, recC2145 and recB2154 is severely reduced to the level of a null recBC allele when combined with a recF, recO or recR mutant allele. Such resistance was also dependent on RecJ and RecQ functions. UV resistance of these non-null recBCD mutants is also reduced by recF, recJ or recQ mutation. These results demonstrate that the RecFOR pathway of recombination can contribute greatly to resistance to RM-mediated host killing, depending on the genetic background.
authors.affiliation: Laboratory of Social Genome Sciences, Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Naofumi
authors.initials: N
authors.lastname: Handa
authors.affiliation: Institute of Medical Science, University of Tokyo, Shirokanedai, Tokyo 108-8639, Japan.|Laboratory of Social Genome Sciences, Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Asao
authors.initials: A
authors.lastname: Ichige
authors.affiliation: Graduate Program in Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Japan.|Institute of Medical Science, University of Tokyo, Shirokanedai, Tokyo 108-8639, Japan.|Laboratory of Social Genome Sciences, Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Ichizo
authors.initials: I
authors.lastname: Kobayashi
mesh_terms: D015169:Colony Count, Microbial; D004268:DNA-Binding Proteins / Q000502:physiology*; D004926:Escherichia coli / Q000201:enzymology* / Q000254:growth & development* / Q000528:radiation effects; D029968:Escherichia coli Proteins / Q000502:physiology*; D043211:Exodeoxyribonuclease V / Q000172:deficiency*; D005090:Exodeoxyribonucleases / Q000502:physiology; D009097:Multienzyme Complexes / Q000502:physiology; D053484:RecQ Helicases / Q000502:physiology; D011995:Recombination, Genetic; D014466:Ultraviolet Rays
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; C081006:RecO protein, E coli; C489318:RecR protein, E coli; C489340:recF protein, E coli; D005090:Exodeoxyribonucleases; C489467:RecJ protein, E coli; D043211:Exodeoxyribonuclease V; C506724:RecQ protein, E coli; D053484:RecQ Helicases