Roles of recA mutant allele (recA495) in frameshift mutagenesis.
The chemical carcinogen N-acetoxy-N-2-acetylaminofluorene (N-AcO-AAF) induces frameshift mutations located within two types of specific sequences (mutation hot spots): i) contiguous guanine sequences and ii) alternating GC sequences. The genetic requirements of these frameshift events were investigated using specific reversion assays. AAF-induced -2 frameshift mutagenesis at alternating GC sequences is peculiar in that it requires a LexA- controlled function which is not UmuDC and occurs in the absence of RecA protein, provided the SOS regulon is derepressed. Moreover, the non-activated form of the RecA protein was shown to act as an inhibitor in this mutation pathway. As we were interested in elucidating this mutation pathway, we have developed a convenient spot reversion assay specific for the detection of this class of mutations. This assay allowed us to isolate E coli mutants affected either in repair or mutagenesis functions. One particular mutant, recA495, is very sensitive to UV and N-AcO-AAF, and is defective in recombination and UV mutagenesis. The RecA495 protein exhibits very low binding to both single- and double-stranded DNA. We show that when the SOS regulon is derepressed, the recA495 allele has two contrasting roles in frameshift mutagenesis: i) it prevents the induction of -1 frameshift mutations at repetitive sequences and ii) it is permissive for the induction of -2 frameshift mutations within alternating GC sequences.
Janel-Bintz
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R
Groupe de Cancérogenèse et de Mutagenèse Moléculaire et Structurale, Institut de Biologie Moléculaire et Cellulaire du CNRS (IBMC), Strasbourg, France.
Maenhaut-Michel
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G
Takahashi
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M
Fuchs
R P
RP
D000483:Alleles; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics*; D016368:Frameshift Mutation; D005798:Genes, Bacterial; D016296:Mutagenesis; D011938:Rec A Recombinases / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid
D011938:Rec A Recombinases