Expression of the cloned bacteriophage phi X174 A* gene in Escherichia coli inhibits DNA replication and cell division.

The A* gene of bacteriophage phi X174 has been cloned into the inducible expression vector pCQV2 under conditions allowing its lethal action to be controlled by the lambda cI857 repressor. Upon induction of expression, DNA synthesis in Escherichia coli carrying the recombinant plasmid is severely inhibited; however, these same cells permit beta-galactosidase induction at a rate similar to that observed in control cells at the inducing (for A*) temperature. Cells in which A* is expressed form filaments and produce more RecA protein, indicating at least a partial induction of the SOS response; however, there is no evidence of damage to the bacterial chromosome. It appears that the A* protein has as one function the inhibition of cell division and DNA replication but not transcription or protein synthesis during phage infection.