Control of deoxyribonucleic acid synthesis in a Bacillus subtilis mutant temperature sensitive for initiation of chromosome replication.

We used a Bacillus subtilis mutant described previously, which is temperature sensitive for initiation of replication. The inhibition of deoxyribonucleic acid synthesis occurring at 45 C was shown to be reversed when the temperature is lowered even in the absence of protein synthesis. If the bacteria are returned to 30 C, after a prior period at 45 C, they are able to initiate the first round of replication in the presence of chloramphenicol, but the initiation of the second round still requires protein synthesis. This paper shows that the proteins necessary to initiate the second round of replication can be present in bacteria long before this round is initiated. In addition, the appearance of these proteins seems to be influenced by the length of the previous 45 C period. Although similar reinitiation kinetics are observed at 30 C after prior 45 C periods of 30 or 65 min, the ability to initiate the second round without further protein synthesis appears much earlier after a longer exposure at 45 C. To explain these results, a hypothesis is presented which assumes that two different proteins are both necessary for initiation. Only one of these proteins could be accumulated at 45 C during the inhibition of deoxyribonucleic acid synthesis. A peculiarity of initiation material in mutant Ts 37 is that it may be active at 45 C if it has been exposed previously at 30 C.