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Multicopy single‐stranded DNAs with mismatched base pairs are mutagenic in Escherichia coli
Author(s) -
Maas Werner K.,
Wang Chi,
Lima Tania,
Zubay Geoffrey,
Lim Dongbin
Publication year - 1994
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1994.tb02178.x
Subject(s) - biology , base pair , mutagenesis , escherichia coli , dna , genetics , mutation , rna , mutant , mutation frequency , dna mismatch repair , microbiology and biotechnology , dna repair , gene
Summary Retrons are genetic elements that encode multicopy single‐stranded DNAs called msONAs. They are clonally distributed in Escherichia coli and retrons in different clones produce DNAs with different nucleotide sequences. msDNAs consist of an RNA molecule covalently linked to a single‐stranded DNA molecule. The latter contains an inverted repeat, resulting in a stem‐loop structure. In two retrons, Ec83 and Ec78, the DNA is cleaved off from the RNA. All known retrons except Ec78, have one or more mismatched base pairs in the stem‐loop structure. We found that two retrons, Ec86 and Ec83, when present in high copy numbers are mutagenic. The ratios of mutation frequencies observed in Lac indicator strains were similar to the ratios observed for a mutant defective in mismatch repair. It is known that some proteins required for mismatch repair bind to mismatched base pairs prior to carrying out repair. The similarity in the mutation frequency ratios suggested that the mutagenesis caused by msDNAs of retrons Ec86 and Ec83 might be due to seqestration of a mismatch repair protein by msDNA. Strong support for this interpretation was obtained from the finding that the msDNA produced by retron Ec78 is not mutagenic.