A Regulatory Gene of Phenylalanine Biosynthesis ( pheR ) in Salmonella typhimurium

Abstract

Fluorophenylalanine-resistant mutants of Salmonella typhimurium were isolated in which synthesis of chorismate mutase P-prephenate dehydratase (specified by pheA) was highly elevated. Transduction analysis showed that the mutation affecting pheA activity was not linked to pheA, and conjugation and merodiploid analysis indicated that it was in the 95to 100-min region of the Salmonella chromosome. Evidence is presented for the hypothesis that the mutation responsible for constitutivity of chorismate mutase P-prephenate dehydratase occurred in pheR, a gene specifying a cytoplasmic product that affected pheA. pheR mutants were found to carry a second mutation, tyrO. The tyrO mutation acts cis to cause increased levels of the tyrosine biosynthetic enzymes 3-deoxy-D-arabinoheptulosonate 7-phosphate synthetase (tyr) and prephenate dehydrogenase, but it has no effect on regulation of pheA.

Regulation of phenylalanine biosynthesis in Escherichia coli K-12: control of transcription of the pheA operon

“…c See Table 2, footnote b. unlikely explanation, as the F116 effect was noted by us with all three of our independent pheR mutations (including one with partial loss of repressor activity) and also by Gollub et al with their pheR mutation in S. typhimurium (7). (ii) The pheR phenotype is produced by the interaction of mutations in two separate genes, and the presence of a functional gene product from either can make a strain pheR+.…”

“…(iii) The third possibility, which appears to be the most likely explanation, is that F116 carries the pheR gene itself. It may be that in some strains of E. coli K- 12 other than those which we tested, the pheR gene is located in the 59to 65-min region (homologous to the map location of pheR in S. typhimurium [7]) and that the parent Hfr from which F116 was derived, AB312, was one such strain, or it may be that the gene pheR has undergone an aberrant translocation from its normal site on the chromosome onto F116. Our experimental results failed to demonstrate any homology between F116 and the chromosomal pheR region, but the tests were genetic in nature and not sensitive enough to exclude the presence of small regions of identity.…”

“…A pheR mutant of Salmonella typhimurium has been obtained (7). This mutation is recessive in heterogenote strains carrying F116 of E. coli K-12, which permitted the direct inference that the gene pheR also exists in E. coli and is on the portion of the chromosome present on F116.…”

tyrR, A Regulatory Gene of Tyrosine Biosynthesis in Salmonella typhimurium

“…1). We recently described and mapped a pheR gene in Salmonella which apparently regulates pheA but not aroG, the gene for DAHP synthetase (phe) (12). On the other hand, we have not observed tyrR mutants in which the aroG product and tyrosine pathway enzymes were simultaneously derepressed.…”

“…Further attempts were made to locate the tyrR mutation in strain SG1 by complementation with E. coli episomes (12). Various F' strains of E. coli were crossed with SG1 derivatives to construct merodiploids which were tested for the presence of tyrR+ allele.…”