Regulation of guaC expression in Escherichia coli

The guaC gene encodes GMP reductase, which converts GMP to inosine monophosphate. Regulation of guaC expression was examined by use of guaC-lac fusions created by Mu d1(lac). In these strains, beta-galactosidase is induced by guanine derivatives, and this induction is prevented by adenine. Our previous implication that glutamine acts as a negative effector of transcription was confirmed by showing that glutamine analogs (diazo-oxo-norleucine and methionine sulfoximine) can also induce beta-galactosidase. GMP was implicated as a likely candidate for the in vivo inducer by introducing a gpt block to prevent the conversion of guanine to GMP and a deoD block to prevent the interconversion of guanine and guanosine. Regulatory mutants were isolated by growth on lactose plus adenine. Though these showed high constitutive levels of beta-galactosidase, they were normal for the regulation of GMP reductase when the fusion was corrected by transduction to guaC+ or when guaC+ was introduced by plasmid complementation. The regulatory mutants were linked to guaC.