No abstract

CI represses cro; Cro represses cI. This double negative feedback loop is the core of the classical CI-Cro epigenetic switch of bacteriophage . Despite the classical status of this switch, the role in development of Cro repression of the P RM promoter for CI has remained unclear. To address this, we created binding site mutations that strongly impaired Cro repression of P RM with only minimal effects on CI regulation of P RM . These mutations had little impact on development after infection but strongly inhibited the transition from lysogeny to the lytic pathway. We demonstrate that following inactivation of CI by ultraviolet treatment of lysogens, repression of P RM by Cro is needed to prevent synthesis of new CI that would otherwise significantly impede lytic development. Thus a bistable CI-Cro circuit reinforces the commitment to a developmental transition.

DNA-dependent RNA polymerase (RNAP) from prokaryotic to eukaryotic cells is conserved in sequence and structure due to the universality of DNA as a store of information and the need to decode this information into protein expression through copying into messenger RNA.