Catabolite modulator factor: physiological properties and in vivo effects.

Catabolite modulator factor (CMF) specifically inhibits the expression of operons sensitive to catabolite repression. Systems known to be catabolite independent are not affected by CMF. The rate of metabolism of CMF depends on the extent of catabolite repression: it is slow under conditions of strong repression and high in catabolically derepressed cells. Cyclic AMP does not interfere with the rate of CMF metabolism. It has been found that a certain class of crp mutants are partially resistant to the repressive effect of CMF. Our results provide considerable support for the existence of an additional negative control in the regulation of catabolite repression.