Positive control of ilvC expression in Escherichia coli K-12; identification and mapping of regulatory gene ilvY

The construction of a plasmid carrying the ilvC::lacZ fusion is described. This plasmid provides a convenient source of template deoxyribonucleic acid for use in an in vitro protein-synthesizing system. We screened strains deleted in regions of the ilv cluster for their ability to support ilvC-dependent beta-galactosidase synthesis. The fact that two deletions prevented beta-galactosidase production indicated that ilv-C expression is under positive control. By use of plasmids carrying the positive-control factor structural gene ilvY, we were able to restore protein-synthesizing ability to these strains. These plasmids also enabled us to map ilvY between ilvA and ilvC.