Miniplasmids of bacteriophage P1. I. Stringent plasmid replication does not require elements that regulate the lytic cycle

Defective prophages of bacteriophage P1Cm that lack about a third of the P1 genome were isolated. The known elements involved in the control of the lytic cycle are eliminated by deletion (c4, ant) or can be rendered non-functional by thermal denaturation (c1-ts) without killing the lysogen. Precise control over plasmid replication and segregation is retained in the absence of these controls on the lytic cycle. It is proposed that the plasmid and lytic cycle modes of P1 replication are regulated by separate mechanisms.