Molecular basis of valine resistance in Escherichia coli K-12.

The relationship of valine resistance to the expression of the ilvGEDA operon of Escherichia coli K-12 has been determined. DNA sequence and in vivo protein analyses indicate that in wild-type E. coli K-12 there is a frameshift site within the gene (ilvG) for valine resistance. The ilvG+2096 (formerly designated ilv02096) mutation displaces this frameshift site, resulting in the expression of ilvG and the relief of transcriptional polarity on the distal genes of this operon. Thus, the "ilv0" mutation, which concomitantly confers valine resistance and increased expression of the ilvEDA genes, is, in fact, the "reversion" of a polar site within the first structural gene of the ilvGEDA operon.