Regulation of lysogeny by the plasmid prophages P1 and P7 is mediated by expression of genes located in the ImmC and ImmI regions of the phage genomes. The c1 and c4 genes (located in ImmC and ImmI, respectively) are both required for the maintenance of lysogeny and are believed to code for repressors of transcription. The structure of ImmI genes (specifically c4, ant/reb, and sim) will be determined by DNA sequence analysis. Gene expression in the ImmC regions will be investigated by identifying transcription products produced in vitro and in vivo and measuring the effect of c1 repressor binding on their expression. The precise nucleotides involved in the interaction of the c1 repressor with its operator sites will be determined by studying repressor binding to synthetic oligonucleotides of defined sequence. The characterization of P1 and P7 regulatory elements should provide insights into control mechanisms operating during bacteriophage infection and plasmid maintenance.
