Replication of Bacteriophage M13: Mechanism of Single‐Strand DNA Synthesis in an Escherichia coli Mutant Thermosensitive in Chromosomal DNA Replication

In Escherichia coli HfrH 165/70 (dnaB) infection with bacteriophage M 13 is abortive at the restrictive temperature of 41°C. However, if the progeny single‐strand synthesis has started at the permissive temperature (34°C), it will continue after a temperature shift by an asymmetric displacement synthesis as shown (a) by the flow of label from replicative form molecules to single strands and (b) by the almost exclusive labeling of the viral strand of the replicative form. Since a pulse label is found first in the membrane fraction and can be chased into the cytoplasm, M 13 single‐strand synthesis may occur at the cell membrane. Also at the elevated temperature, it is inhibited by rifampicin and chloramphenicol. Whereas rifampicin stops the synthesis of phage‐specific DNA immediately, chloramphenicol causes the conversion of newly synthesized single strands into double‐stranded replicative form molecules. This demonstrates that not only the synthesis of M 13 single strands but also their conversion into double strands is possible even in the absence of the dnaB function. Therefore for these types of DNA replication, contrary to the semiconservative replication of double‐stranded DNA, the product of the dnaB gene is not required.