Timing and other features of the action of the ts1 division initiation gene product of Bacillus subtilis.

The ts1 division initiation mutation of Bacillus subtilis 160 was transferred into a thymine-requiring strain of B. subtilis 168. Aspects of the role and timing of the action of the ts1 gene product in relation to septum formation were studied by comparing the behavior of this new strain with that of the isogenic wild type after outgrowth of germinated spores. The ts1 gene product was shown to be required for the asymmetric division which occurs in the absence of chromosome replication, in addition to normal division septation. The time interval between completion of the action of the ts1 gene product and initiation of the first central division septum was estimated to be less than 4 min at 34 degrees C, and it is possible that an active ts1 gene product is required until the commencement of septal growth. Recovery of septa after transfer of outgrown spores (filaments) from the nonpermissive to the permissive temperature was also examined. During recovery, septa formed at sites which were discrete fractional lengths of the filaments, with the first septum located at the most polar of these sites. The data have been interpreted in terms of the formation of potential division sites at the nonpermissive temperature and the preferred utilization, upon recovery, of the most recently formed site. Recovery of septa at the permissive temperature occurred in the absence of DNA synthesis but was blocked completely by inhibitors of RNA and protein synthesis. It is possible that the only protein synthesis required for recovery of septa is that of the ts1 gene product itself.