Starvation for ilvB operon leader amino acids other than leucine or valine does not increase acetohydroxy acid synthase activity in Escherichia coli.

Eleven different amino acids are encoded in the ilvB leader mRNA. Starvation for leucine or valine, but not for any of the other nine amino acids, resulted in high levels of acetohydroxy acid synthase I. These results are discussed in terms of a report (C.A. Hauser and G.W. Hatfield, Proc. Natl. Acad. Sci. U.S.A. 81:76-79, 1984) which suggests that threonine and alanine, in addition to leucine and valine, are involved in the regulation of the ilvB operon.