Growth inhibition of Escherichia coli K-12 by L-valine: a consequence of a regulatory pattern

We studied the production of the ilvG gene product, the valine resistant acetolactate synthase isoenzyme II, in an ilvO+ G+ ilvB ilvHI derivative of Escherichia coli K-12. This strain contains mutations in the structural genes for the valine sensitive acetolactate synthase isoenzymes I and III. We find that the ilvG gene is not expressed in this strain when gworn with either isoleucine and valine or with isoleucine, leucine and valine, or when limited for either isoleucine or valine. Since we previously found that the ilvG gene is expressed in an ilvO603 containing strain (Favre et al., 1976), we presume that the mechanism by which E. coli K-12 regulates the ilv gene cluster is responsible for the lack of ilvG expression in the ilvO+ strain. The valine sensitivity of E. Coli K-12 is a consequence of this regulatory pattern.