NEW MAP LOCATION OF ILVO IN ESCHERICHIA-COLI

Abstract

Mutations in ilvO, the operator site for operon A of the ilv region of E. coli K-12, are reported to cause a cis dominant derepression of the operon A gene products and to map between ilvC and ilvA. The F25 episome which does not carry the region between ilvC and ilvA but only ilvE, ilvD and a part of ilvA, can transfer ilvO genetic material. Genes of operon A on the F25 episome respond normally to a derepression signal. The ilvO is probably on the F25 episome. Five-point crosses demonstrate that mutations in ilvO map nearer to ilvE than to ilvA. The gene order in the ilv region is probably CADEO, not COADE, with transcription and translation in operon A being from ilvE to ilvA not ilvA to ilvE. Mutations in ilvO cause a cis dominant derepression of the operon A gene products but mutations in ilvO lead to an AHAS [acetohydroxyacid synthetase] activity more resistant to inhibition by valine than that of the present O+ strain.