Role of the purine repressor in the regulation of pyrimidine gene expression in Escherichia coli K-12

Abstract

The pyrC and pyrD genes of Escherichia coli K-12 encode. the pyrimidine biosynthetic enzymes dihydroorotase and dihydroorotate dehydrogenase, restively. A highly conserved sequence in the promoter regions of these two genes is similar to the pur operator, which is the binding site for the purine repressor (PurR). In this study, we examined the role of PurR in the regulation ofpyrC and pyrD expression. Our results show that pyrC and pyrD expression was repressed approximately twofold in cells grown in the presence of through a mechanism requiring PurR. A mutation, designated pyrCp926, which alters a 6-base-pair region within the conserved sequence in the pyrC promoter elimted PurR-mediated repeession ofpyiC expression. This result indicates that PurR binds to the pyiC (and presumably to the pyrD) conserved sequence and inhibits transcriptional initiation. We also demonstrated that the pyrCp926 mutation had no effect on pyrimidinemediated regutation of pyrC expression, indicating that pyrimidine and purine effectors act through independent mechanisms to control the expression of the pyrC and pyrD genes.

Translational control of pyrC expression mediated by nucleotide-sensitive selection of transcriptional start sites in Escherichia coli

“…Residual regulation is never less than 1. transcriptional initiation under both conditions is essentially the same. Another explanation could be that the low-level regulation is caused by purine repressor-mediated inhibition of pyrC transcriptional initiation, which was recently described (4,33). Arguing against this possibility is the fact that the full range of pyrimidine-mediated regulation of pyrC expression can occur in a mutant strain in which the purine repressor cannot bind to the pyrC promoter region (33).…”

“…Individual pyrC mutations were ments were separated by either polyacrylamide or agarose constructed in the recombinant bacteriophage M13mp9-gel electrophoresis. DNA was purified from polyacrylamide amC5 by using the gapped heteroduplex method of oligonugel slices as previously described (18) and further purified by cleotide-directed mutagenesis essentially as described by salt elution from a DEAE-cellulose (Whatman DE52) colWilson and Turnbough (33). The presence of each mutation umn.…”

“…1) with the equivalent fragment isolated from the replicative form of the mutagenized bacteriophage M13mp9amC5. The mutations were introduced into the chromosome of strain CLT68 by homologous recombination as previously described (33), with the following modifications. Strain CLT114 (recD pyrC) was the recipient strain and was transformed to pyrimidine prototrophy with linearized plasmid DNA by electroporation as described previously (27).…”

“…The presence of each mutation on the chromosome was verified by amplifying the pyrC promoter-regulatory region of transformants by using the polymerase chain reaction (5) and determining the DNA sequence of the amplified products. Southern hybridization was performed to demonstrate that no large insertions, deletions, or rearrangements occurred during the introduction of each mutation (33).…”

Regulation of levels of purine biosynthetic enzymes in Bacillus subtilis: effects of changing purine nucleotide pools

“…This sequence is found in the -35 region of purine biosynthetic genes (He et al, 1990). The PurR protein has been shown also to repress the pyrC gene (dihydroorotase) of pyrimidine biosynthesis in S. typhimurium (Neuhard et al, 1990) and E. coli Wilson & Turnbough, 1990). Involvement of GTP in expression of other genes of the pyrimidine biosynthesis pathway has also been observed (Jensen, 1989).…”