THE REQUIREMENT FOR MOLECULAR CHAPERONES IN LAMBDA-DNA REPLICATION IS REDUCED BY THE MUTATION-PI IN LAMBDA-P GENE, WHICH WEAKENS THE INTERACTION BETWEEN LAMBDA-P PROTEIN AND DNAB HELICASE

During the initiation of lambda DNA replication, the host DnaB helicase is complexed with phage lambda P protein in order to be properly positioned near the ori lambda-lambda O initiation complex, However, the lambda P-DnaB interaction inhibits the activities of DnaB, Thus, the concerted action of bacterial heat shock proteins, DnaK, DnaJ, and GrpE, is required to activate the helicase. Wild-type phage lambda cannot grow on the E, coli dnaB, dnaK dnaJ, and grpE mutants, However, lambda phage with a mutation pi in the lambda P gene, is able to produce progeny in these mutants as well as in the wild-type bacteria, Purified mutant lambda pi protein reveals a much lower affinity to DnaB than wildtype lambda P, and the lambda pi-DnaB complex is unstable, Also, a very low concentration of DnaK protein is sufficient to activate the helicase in a replication system based on lambda dv dsDNA. In that system, the mutant DnaK756 protein, inactive in the lambda P-dependent replication, revealed its activity in the lambda pi-dependent reaction, The lambda O-lambda P-dependent replication system based on M13 ssDNA efficiently replicates DNA in the absence of any chaperone protein, unless lambda P is substituted by the lambda pi mutant protein, Data presented in this paper explain why lambda pi phage is able to grow on wild-type and dnaK756 bacteria.