A recombinant plasmid was constructed which carries bacteriophage λ initiator genes O and P under control of tandemly arranged pL and pR promoters. These promoters were repressed by a thermosensitive repressor, cI857, at low temperature, but became active when the culture was incubated at 42° C. Upon elevation of the temperature, the O and P proteins were overproduced to the extent that they constituted several per cent of the total E. coli cellular proteins. Both the O and P proteins have been purified to apparent homogeneity, and were shown to consist of 298 and 233 amino acid residues, respectively. The amino acid composition and the terminal partial amino acid sequence of each protein were determined. Through these analyses, the locations of the O and P genes in the known λ DNA sequence were determined. The termination codon for the O gene overlaps with the initiation codon for the P gene. The purified O protein binds specifically to the replication origin of λ (λ ori) in accordance with our previous observations. The purified P protein inhibits an ATPase activity of dnaB protein.
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