A new role for Escherichia coli Dam DNA methylase in prevention of aberrant chromosomal replication.

ABSTRACT: The Dam DNA methylase of Escherichia coli is required for methyl-directed mismatch repair, regulation of chromosomal DNA replication initiation from oriC (which is DnaA-dependent), and regulation of gene expression. Here, we show that Dam suppresses aberrant oriC-independent chromosomal replication (also called constitutive stable DNA replication, or cSDR). Dam deficiency conferred cSDR and, in presence of additional mutations (?tus, rpoB*35) that facilitate retrograde replication fork progression, rescued the lethality of ?dnaA mutants. The DinG helicase was required for rescue of ?dnaA inviability during cSDR. Viability of ?dnaA dam derivatives was dependent on the mismatch repair proteins, since such viability was lost upon introduction of deletions in mutS, mutH or mutL; thus generation of double strand ends (DSEs) by MutHLS action appears to be required for cSDR in the dam mutant. On the other hand, another DSE-generating agent phleomycin was unable to rescue ?dnaA lethality in dam+ derivatives (mutS+ or ?mutS), but it could do so in the dam ?mutS strain. These results point to a second role for Dam deficiency in cSDR. We propose that in Dam-deficient strains, there is an increased likelihood of reverse replication restart (towards oriC) following recombinational repair of DSEs on the chromosome.

SUBMITTER: Raghunathan N 

PROVIDER: S-EPMC6582345 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature