Gene that controls initiation of chromosome replication and prophage induction in Bacillus subtilis

Abstract

THE mechanism of initiation of the chromosome replication cycle in bacteria is beginning to be elucidated by genetic and biochemical studies1–3. But little is known about what controls the initiation frequency which has a key role in regulating the rate of DNA synthesis in response to the change in bacterial growth rate4,5. The existence of such a regulatory entity—initiator—synthesised in harmony with the increase in cell mass or the change in the cell or replication cycle, has been hypothesised6,7. We have investigated the nature of the hypothetical regulator, based on the assumption that the induction of prophage and the initiation of host cell chromosome replication would be controlled by a common regulator directly or indirectly. The assumption is based on observations that the inducibility of prophages and the initiation frequency of chromosome replication share common features in their responses to the bacterial growth rate and to the inhibition of DNA replication4,5,8–10. We assumed that the regulatory material, substance X, accumulates in the cell depending on growth rates and is consumed to initiate each replication cycle, and that an unbalanced accumulation of X caused by the inhibition of DNA synthesis would provoke prophage induction. If this assumption is correct it should be possible to isolate conditional mutants in which both the initiation of chromosome replication and prophage induction are prevented in non-permissive conditions.