Genetic control of raffinose utilization in Escherichia coli.

The genetic and physiological control of ,(galactosidase in Escherichia coli has been the subject of extensive investigations. It has been clearly shown that the presence of this inducible enzyme is dependent on the genic constitution of the cell (Lederberg et al., 1951). In many cases gene mutation has led to a complete loss of ability by the cell to produce the enzyme; in other instances a decrease in the amount of enzyme produced was noted. With some lactose mutants a lack of ability of certain inducers to promote the formation of f-galactosidase was observed, and in one instance (Rickenberg, 1954) was shown to be associated with a decreased permeability to lactose. However, no clear evidence demonstrating a genic control over inducer specificity rather than innate ability to form enzyme has been presented. The formation of ,B-galactosidase in E. coli strain K-12 can be induced by galactose and many 03-galactosides (Monod et al., 1951; Lester and Bonner, 1952). Neolactose (altrose-3-Dgalactoside ) is an exceptional substrate, for it is not an inducer of the enzyme; neolactose utilizing strains have been shown to be constitutive 3-galactosidase producers (Lederberg, 1951). Some a-galactosides, such as melibiose, are also effective inducers of 3-galactosidase, but raffinose, although containing a melibiose moiety, is ineffective as an inducer and as a carbon source (Monod et al., 1951; Lester and Bonner, 1952). a-Galactosidase has been shown to be induced by galactose and some ac-galactosides, but the ability of ,B-galactosides to induce a-galactosidase appears to depend on the strain of E. coli used. Thus, Porter et al. (1953) report that, with E. coli strain B, lactose can serve as an inducer of a-galactosidase, whereas, in our experience, lactose is ineffective as an inducer in K-12.