Regulation of the gal Operon of Escherichia coli by the capR Gene

We have examined in greater detail the derepression of uridine diphosphate galactose-4-epimerase synthesis in capR mutants of Escherichia coli first observed by Markovitz. (Markovitz, A. (1964) Proc. Nat. Acad. Sci. U. S. A. 51, 239–246). All three enzymes of the gal operon are derepressed from 2- to 4-fold by this mutation. This derepression may be superimposed on the conventional derepression seen when the gal operon is induced with fucose or by a regulatory mutation. Measurement of the level of gal messenger ribonucleic acid indicates that the derepression caused by the capR mutation probably occurs at the level of transcription since there is a coordinate increase in gal enzyme activity and in the level of gal mRNA. The effect of the capR mutation on the gal operon appears to be independent of cyclic 3',5'-monophosphate or glucose-mediated repression. Thus the product of the capR locus behaves as if it is an additional negative control element affecting the expression of the gal operon.