Alternate Pathways of Bacteriophage M 13 DNA Replication

Abstract

The replication of bacteriophage M 13 provides an excellent system for studying different types of DNA synthesis. The replication of M 13 DNA occurs in three temporally separated steps (Marvin & Hohn, 1969). First the infecting single stranded phage DNA is converted into a double stranded replicative form (RF) by the synthesis of a complementary strand. Early in the infection the replicative forms multiply by symmetric semi-conservative replication to form a pool of replicative form molecules. Later double strand synthesis stops and single stranded viral DNA is produced by an asymmetric replication process in which the viral strand of the replicative form is displaced as a new one is synthesized (Ray, 1969). These processes depend largely on host proteins. Only two phage genes are involved in DNA replication (Pratt, 1969): Gene-2 is required for double strand replication as well as for single strand synthesis possibly by coding for a “nickase” (Lin & Pratt, 1972; Tseng & Marvin, 1972; Fidanian & Ray, 1972). The gene-5 protein is involved only in single stranded DNA synthesis (Salstrom & Pratt, 1972).