Genetic and biochemical studies of the guanosine 5′-monophosphate pathway in Escherichia coli

Abstract

Three genes which are involved in the guanosine 5′-monophosphate cycle of Escherichia coli were mapped on the chromosome. The genes guaA and guaB were located by transduction with phage Pikc, the guaC gene by conjugation. The guaA and guaB loci have been mapped between the genes for tyrosine and histidine biosythesis; they are clustered and their order is from the tyrosine locus, guaA-guaB. The guaC locus was mapped on quite another part of the chromosome, in the thr-leu region.

Enzyme levels of guaA− and guaB− strains, grown under various conditions of repression and derepression, were determined. The results showed a coordinate control of the synthesis of inosine-5′-monophosphate dehydrogenase (EC 1.2.1.14) and xanthosine-5′-monophosphate aminase (EC 6.3.4.1). Guanosine-5′-monophosphate reductase (EC 1.6.6.9), however, is not coordinately regulated with these two enzymes. It is suggested that guaA and guaB are structural genes of one operon.