Back to the future: the new ICE age.

The analysis of bacterial genomes has revealed an extraordinary array of conjugal elements (integrative and conjugative element or ICE) that reside in bacterial chromosomes. These elements contribute to the pan-genomes of individual species and confer a wide variety of properties on their bacterial hosts. ICEBs1 is a conjugal element found in Bacillus subtilis that has a remarkable regulatory mechanism that apparently favours conjugation when there are suitable recipient bacteria at high density or when the bacterial host is facing DNA-damaging stresses. In the current issue, Bose et al. dissect the mechanism of induction of transfer of this element, and reveal a new, apparently widespread repressor anti-repressor system and a new mechanism of repressor destruction by proteolysis.