Molecular cloning of genes involved in purine biosynthetic and salvage pathways of Salmonella typhimurium

Genes have been cloned from Salmonella typhimurium which when present on the multicopy plasmid pBR322 in the E. coli strain NT31 confer a Gua⁺ phenotype on this strain. NT31 is a purE gpt double mutant and it was expected that a Gua⁺ phenotype could be conferred on it by the cloning of either gpt or purE. It was, however found that in addition to these two loci the molecular cloning of another gene, which has been identified as hpt, in pBR322 confers a Gua⁺ phenotype on NT31. This result is explained by the overproduction of the hpt gene product, hypoxanthine phosphoribosyl transferase, which compensates for the lack of the gpt product guanine-xanthine phosphoribosyl transferase. Restriction analysis of the three loci, gpt, hpt and purE is also presented.