lon incompatibility associated with mutations causing SOS induction: null uvrD alleles induce an SOS response in Escherichia coli.
The uvrD gene in Escherichia coli encodes a 720-amino-acid 3'-5' DNA helicase which, although nonessential for viability, is required for methyl-directed mismatch repair and nucleotide excision repair and furthermore is believed to participate in recombination and DNA replication. We have shown in this study that null mutations in uvrD are incompatible with lon, the incompatibility being a consequence of the chronic induction of SOS in uvrD strains and the resultant accumulation of the cell septation inhibitor SulA (which is a normal target for degradation by Lon protease). uvrD-lon incompatibility was suppressed by sulA, lexA3(Ind(-)), or recA (Def) mutations. Other mutations, such as priA, dam, polA, and dnaQ (mutD) mutations, which lead to persistent SOS induction, were also lon incompatible. SOS induction was not observed in uvrC and mutH (or mutS) mutants defective, respectively, in excision repair and mismatch repair. Nor was uvrD-mediated SOS induction abolished by mutations in genes that affect mismatch repair (mutH), excision repair (uvrC), or recombination (recB and recF). These data suggest that SOS induction in uvrD mutants is not a consequence of defects in these three pathways. We propose that the UvrD helicase participates in DNA replication to unwind secondary structures on the lagging strand immediately behind the progressing replication fork, and that it is the absence of this function which contributes to SOS induction in uvrD strains.
SaiSree
L
L
Centre for Cellular and Molecular Biology, Hyderabad 500 007, India.
Reddy
M
M
Gowrishankar
J
J
D049069:ATP-Dependent Proteases; D000251:Adenosine Triphosphatases / Q000235:genetics*; D000483:Alleles; D001483:Base Sequence; D004265:DNA Helicases / Q000235:genetics*; D004258:DNA Polymerase III / Q000235:genetics; D004260:DNA Repair; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics; D006360:Heat-Shock Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D049070:Protease La; D011995:Recombination, Genetic; D051716:Replication Protein A; D013014:SOS Response, Genetics / Q000235:genetics*; D012697:Serine Endopeptidases / Q000235:genetics*; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics; D013489:Suppression, Genetic
D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D051716:Replication Protein A; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499294:dam protein, E coli; C065639:DNA polymerase A; D004258:DNA Polymerase III; C468316:dnaQ protein, E coli; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La; D000251:Adenosine Triphosphatases; C506746:UvrD protein, E coli; C506743:priA protein, E coli; D004265:DNA Helicases