A CHECKPOINT INVOLVING RTP, THE REPLICATION TERMINATOR PROTEIN, ARRESTS REPLICATION DOWNSTREAM OF THE ORIGIN DURING THE STRINGENT RESPONSE IN BACILLUS-SUBTILIS

Regulation of DNA replication in Bacillus subtilis involves a post-initiation mechanism which is subject to control by the Stringent System, an essential regulatory network, mediated by the alarmone, ppGpp. In detailed studies using DNA-DNA hybridization procedures, we have now shown that, following the induction of the Stringent Response, replication is blocked downstream of the origin, on the left, close to the hot marker (-175 kb) and on the right, beyond the soft10 marker (+199 kb), In addition, we provide evidence that inhibition of replication under these conditions requires the replication terminator protein (RTP), In a mutant lacking RTP, a protein normally involved in termination of chromosomal replication through recognition of specific terminator sequences, replication continues past the sites normally blocked by the Stringent Response, These data strengthen the argument that this second level of control of DNA replication occurs at specific sites, the Stringent Terminus (STer) sites, either side of oriC, Such sites are presumably related to the sequence involved in RTP recognition at the terminus, terC. We propose that the binding of RTP must be modulated, perhaps through the action of ppGpp, to recognize postinitiation control sequences during the Stringent Response, in order to block replisome movement. This, therefore, acts as a checkpoint in chromosome elongation.