THE TRIPARTITE IMMUNITY SYSTEM OF PHAGES P1 AND P7

Prophages P1 and P7 exist as unit copy DNA plasmids in the bacterial c ell. Maintenance of the prophage state requires the continuous express ion of two repressors: (i) C1 is a protein which negatively regulates the expression of lytic genes including the C1 inactivator gene coi, a nd (ii) C4 is an antisense RNA which specifically inhibits the synthes is of an anti-repressor Ant. In addition, C1 repression is strengthene d by Ire encoding an auxiliary repressor protein. The repressors C1, C 4 and Lxc are components of a tripartite immunity system of the two ph ages. Here, the mode of action of these regulatory components includin g their antagonists Coi and Ant is described.