Cleavage of λ repressor and synthesis of RecA protein induced by transferred UV-damaged F sex factor

Abstract

Transfer of a UV-damaged F sex factor to a recipient λ lysogen induces prophage λ development. Under these conditions RecA protein synthesis was induced and λ repressor cleaved, as observed upon direct induction, that is, when the recipient λ lysogen was directly exposed to UV-light. The efficiency of induction of RecA protein synthesis in recipient bacteria which had received an irradiated F-lac factor was about 80% of that measured upon direct induction. We observed the simultaneous disappearance of λ repressor and a slight production of cleavage fragments; quantitation by densitometric scanning of the autoradiogram after correction for the efficiency of transfer indicated that 55% of λ repressor was cleaved. Transfer of UV-damaged Hfr DNA failed to induce RecA protein synthesis. A λ phage vector carrying oriF, the cloned origin of F plasmid replication, after exposure to UV-light and infection of a recipient lysogen, induced RecA protein synthesis and a moderate but significant cleavage of λ repressor. Indirect induction by UV-damaged F sex factor or phage λoriF resulted in biochemical cellular reactions similar to those observed upon direct induction. LexA repressor that negatively controls RecA protein synthesis appeared more susceptible to cleavage than did λ repressor.