Characterization of the hemA-prs region of the Escherichia coli and Salmonella typhimurium chromosomes: identification of two open reading frames and implications for prs expression

Abstract

~~ ~~Theprs gene, encoding phosphoribosylpyrophosphate synthetase, is preceded by a leader, which is 302 bp long in Escherichia coli and 417 bp in Salmonella typhimurium. A potential open reading frame (ORF) extends across the prs promoter and into the leader. The region between the prs coding region and an upstream gene (hemA) in E. coli and S. typhimurium was cloned, sequenced and shown to encode two ORFs of unknown function. ORF 1 encodes a 23 kDa protein and ORF 2 a 31 kDa protein, as observed by denaturing PAGE of extracts of cells bearing plasmids encoding the Oms. Both ORFs are transcribed in the same direction as theprs gene with ORF 2 extending into the prs leader. Northern blot analysis showed that the prs message in E. coli was on 1.3 and 2.7 kb transcripts. The shorter transcript encoded theprs gene only, while the longer transcript also encoded the two ORFs. Thus, the prs gene is transcribed from two promoters, the first promoter (PI) originating upstream of ORF 1, and expressing the prs gene in a tricistronic operon and a second promoter (PJ, located within the ORF 2 coding frame, which transcribes the prs gene only. The transcripts encoding prs only were 20 times as abundant as the tricistronic transcripts under all conditions examined. This was the case whether cells containing plasmid-encoded or only chromosomally encoded copies of the hernA-prs region were probed for these transcripts. Derepression of the prs gene upon pyrimidine starvation was shown to be due to an increase in the amount of message originating from the promoter P,.

Phosphoribosyl Diphosphate (PRPP): Biosynthesis, Enzymology, Utilization, and Metabolic Significance

“…A smaller transcript initiates within the ispE coding sequence and contains the last 152 nucleotides of the ispE coding sequence in both organisms. The transcription start site of the smaller transcript and a rho-independent termination site downstream of the prs coding sequence have been mapped (45,397). The smaller transcript is 20-fold more abundant than the larger transcript.…”

“…The smaller transcript is 20-fold more abundant than the larger transcript. Pyrimidine-mediated prs gene regulation occurs via increased amounts of the smaller transcript (397). The coding region of the prs gene is preceded by a leader sequence 302 nucleotides long in E. coli and 417 nucleotides long in S. enterica (45,397,398).…”

“…Pyrimidine-mediated prs gene regulation occurs via increased amounts of the smaller transcript (397). The coding region of the prs gene is preceded by a leader sequence 302 nucleotides long in E. coli and 417 nucleotides long in S. enterica (45,397,398). Comparison of the two leader sequences revealed 149 almost-identical nucleotides of the 5= end of the transcripts of the two organisms, followed by 115 nucleotides in the S. enterica prs leader that are not present in the E. coli prs leader and 152 nucleotides which are almost identical in the leaders of the two transcripts, i.e., an a-b-c arrangement in S. enterica and an a-c arrangement in E. coli.…”

Transcription of the glutamyl-tRNA reductase (hemA) gene in Salmonella typhimurium and Escherichia coli: role of the hemA P1 promoter and the arcA gene product

“…The two maps are aligned by using the N terminus of the hemA gene. The S. typhimurium genome has two insertions of Ϸ100 bp with respect to the E. coli sequence: one in the hemA promoter region and one in the orf2-prsA intergenic region (12,33). (B) DNA sequence of the hemA promoter region in S. typhimurium and E. coli.…”

Biosynthesis of terpenoids: YchB protein of Escherichia coli phosphorylates the 2-hydroxy group of 4-diphosphocytidyl-2C-methyl- d -erythritol

“…2). Post et al (25) tentatively assigned this region as an ATP-binding site. The amino acid sequence of the YchB protein shows some similarity to other kinases, such as homoserine or mevalonate kinases.…”