AN ALTERNATIVE DNA INITIATION PATHWAY IN E. coli

Abstract

ABSTRACT The sdrA102 mutation confers upon cells the ability to replicate DNA in the absence of protein synthesis. The mutation maps near metD . When this mutation was combined with the recA200 mutation which renders the recA protein thermolabile, it had little effect on normal replication. However, the sdrA102 recA200 double mutant exhibited temperature-sensitive stable DNA replication: it continuously replicated DNA in the presence of chloramphenicol at 30°C, whereas at 42°C the DNA content increased only 40–45% before DNA synthesis ceased. Suppressor mutations ( rin ; r ecA-independent) capable of stable DNA replication at 42°C were isolated in the double mutant. The rin mutations specifically suppressed the recA + dependence of stable DNA replication and did not alleviate the defective characteristics of of the recA56 mutants, i.e. the deficient general recombination, extreme UV sensitivity and inability of prophage induction. It was also found that the sdrA102 mutation is replicon-specific: i.e., the mutation allows only replication of the bacterial chromosome but not replication of F plasmid DNA in the absence of protein synthesis. A model is proposed in which the sdrA + gene product is viewed as a repressor of a switch from normal replication to an alternative replication pathway.