Chromosomal lesion suppression and removal in Escherichia coli via linear DNA degradation.
RecBCD is a DNA helicase/exonuclease implicated in degradation of foreign linear DNA and in RecA-dependent recombinational repair of chromosomal lesions in E. coli. The low viability of recA recBC mutants vs. recA mutants indicates the existence of RecA-independent roles for RecBCD. To distinguish among possible RecA-independent roles of the RecBCD enzyme in replication, repair, and DNA degradation, we introduced wild-type and mutant combinations of the recBCD chromosomal region on a low-copy-number plasmid into a DeltarecA DeltarecBCD mutant and determined the viability of resulting strains. Our results argue against ideas that RecBCD is a structural element in the replication factory or is involved in RecA-independent repair of chromosomal lesions. We found that RecBCD-catalyzed DNA degradation is the only activity important for the recA-independent viability, suggesting that degradation of linear tails of sigma-replicating chromosomes could be one of the RecBCD's roles. However, since the weaker DNA degradation capacity due a combination of the RecBC helicase and ssDNA-specific exonucleases restores viability of the DeltarecA DeltarecBCD mutant to a significant extent, we favor suppression of chromosomal lesions via linear DNA degradation at reversed replication forks as the major RecA-independent role of the RecBCD enzyme.
Miranda
Anabel
A
Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA.
Kuzminov
Andrei
A
D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics*; D043211:Exodeoxyribonuclease V / Q000235:genetics* / Q000378:metabolism; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism
D004247:DNA; D011938:Rec A Recombinases; D043211:Exodeoxyribonuclease V