Yet another way that phage manipulates its Escherichia coli host: rexB is involved in the lysogenic-lytic switch

The life cycle of phage has been studied extensively. Of particular interest has been the process leading to the decision of the phage to switch from lysogenic to lytic cycle. The principal participant in this process is the cI repressor, which is cleaved under conditions of DNA damage. Cleaved cI no longer acts as a repressor, allowing phage to switch from its lysogenic to lytic cycle. The well-known mechanism responsible for cI cleavage is the SOS response. We have recently reported that the Escherichia coli toxin-antitoxin mazEF pathway inhibits the SOS response; in fact, the SOS response is permitted only in E.coli strains deficient in the expression of the mazEF pathway. Moreover, in strains lysogenic for prophage , the SOS response is enabled by the presence of rexB. RexB had previously been found to inhibit the degradation of the antitoxin MazE, thereby preventing the toxic action of MazF. Thus, phage rexB gene not only safeguards the prophage state by preventing death of its E.coli host but is also indirectly involved in the lysogenic-lytic switch.