Allele specificity of theEscherichia coli dnaA gene function in the replication of plasmids derived from phageλ

We demonstrate a variation in the effects of seven alleles of theEscherichia coli dnaA gene, which cause temperature sensitivity of initiation of chromosomal replication, on the replication ofλ phage-derived plasmids at 30° C. These mutants showed no allele specificity ofdnaA function in replication of either of twoλπ plasmids studied. On the other hand, the inability of theλP+ plasmid to replicate indnaA508, 46 and204 cells, indnaB (groP A15) or in cells that are temperature sensitive for the chaperone genesdnaK756, dnaJ259 andgrpE280 and 30° C was suppressible by a singleπ mutation. This suggests that it is a common property of theπ protein, probably its weaker interaction with DnaB helicase, that is responsible for the suppression. One can also conclude that the DnaA-regulated transcriptional activation oforiλ acts at the step, in which all these gene products cooperate, i.e. during preprimosome loading and chaperone-mediated release of DnaB from P protein inhibition.