Identification of a high-copy-number plasmid suppressor of a lethal phenotype caused by mutant DnaA protein which has decreased intrinsic ATPase activity

The induction of a mutant DnaA protein (DnaA E204Q) with decreased intrinsi c ATPase activity in cells causes a lethal phenotype, Eased on our results that the decreased ATPase activity of DnaA E204Q is activated to the level of a wild-type protein in the presence of partially purified stimulating fa ctors for DnaA ATPase, we tested the hypothesis that genes encoding the sti mulating factors can be cloned as high-copy-number plasmid suppressors for the lethality caused by DnaA E204Q. We isolated a number of high copy-numbe r plasmids that suppress the lethal phenotype. The genes responsible for th e suppression of the lethal phenotype were revealed to be dnaN, relA, pcnB and cyaA by subcloning, and a site-directed mutational analysis. The mechan isms by which these genes suppressed the lethal phenotype were examined in vivo and in vitro.