The stringent response blocks DNA replication outside the ori region in Bacillus subtilis and at the origin in Escherichia coli

When the Bacillus subtilis dnaB37 mutant, defective in initiation, is returned to permissive temperature after growth at 45 degrees C, DNA replication is synchronized. Under these conditions, we have shown previously that DNA replication is inhibited when the Stringent Response is induced by the amino acid analogue, arginine hydroxamate. We have now shown, using DNA-DNA hybridization analysis, that substantial replication of the oriC region nevertheless occurs during the Stringent Response, and that replication inhibition is therefore implemented downstream from the origin. On the left arm, replication continues for at least 190 x 10(3) base-pairs to the gnt gene and for a similar distance on the right arm to the gerD gene. When the Stringent Response is lifted, DNA replication resumed downstream from oriC on both arms, confirming that DNA replication is regulated at a post-initiation level during the Stringent Response in B. subtilis. Resumption of DNA synthesis following the lifting of the Stringent Response did not require protein or RNA synthesis or the initiation protein DnaB. We suggest, therefore, that a specific control region, involving Stringent Control sites, facilitate reversible inhibition of fork movement downstream from the origin via modifications of a replisome component during the Stringent Response. In contrast, in Escherichia coli, induction of the Stringent Response appears to block initiation of DNA replication at oriC itself. No DNA synthesis was detected in the oriC region and, upon lifting the Stringent Response, replication occurred from oriC. Post-initiation control in B. subtilis therefore results in duplication of many key genes involved in growth and sporulation. We discuss the possibility that such a control might be linked to differentiation in this organism.