THE TUM PROTEIN OF COLIPHAGE-186 IS AN ANTIREPRESSOR

The tum gene of coliphage 186, encoded on a LexA controlled operon, is essential for UV induction of a 186 prophage. Primer extension analys is is used to confirm that Tnm is the sole phage function required for prophage induction and that it acts against the maintenance repressor , GI, to relieve repression of the lytic promoters, P-R and p(B), and thereby bring about lytic development. In vitro experiments with purif ied proteins demonstrate that Tum prevents CH binding to its operator sites. Tum does not compete with CI for binding sites on DNA, and unli ke RecA mediated induction of lambda prophage, the action of Tum on CI is reversible, Mechanisms by which Tum may act against CI are discuss ed.