title: Regulation of the Bacillus subtilis pyrimidine biosynthetic (pyr) gene cluster by an autogenous transcriptional attenuation mechanism.
abstract: A complete transcript of the Bacillus subtilis pyr operon contains the following elements in 5' to 3' order: a 151-nucleotide (nt) untranslated leader; pyrR, encoding a 20-kDa protein; a 173-nt intercistronic region; pyrP, encoding a 46-kDa protein; a 145-nt intercistronic region; and eight overlapping cistrons encoding all of the six enzymes for de novo pyrimidine biosynthesis. Transcription is controlled by the availability of pyrimidines via an attenuation mechanism. There are three transcription terminators within the operon, each of which is preceded by another stem-loop structure, the antiterminator, whose formation would prevent formation of the terminator stem-loop. These are located in the leader, the pyrR-pyrP intercistronic region, and the pyrP-pyrB intercistronic region. Northern (RNA) blot analysis has identified transcripts of lengths which coincide with termination at these proposed attenuation sites and whose relative abundances vary in the expected pyrimidine-dependent manner. Each antiterminator contains a 50-base conserved sequence in its promoter-proximal half. Various transcriptional fusions of the pyr promoter and surrounding sequences to promoterless reporter genes support an attenuation mechanism whereby when pyrimidines are abundant, the PyrR protein binds to the conserved sequence in the pyr mRNA and disrupts the antiterminator, permitting terminator hairpin formation and promoting transcription termination. Deletion of pyrR from the chromosome resulted in the constitutive, elevated expression of aspartate transcarbamylase, which is encoded by pyrB, the third gene in the operon. Complementation of an E. coli upp mutant, as well as direct enzymatic assay, has demonstrated that pyrR also confers uracil phosphoribosyltransferase activity. Analysis of pyrR and upp deletion mutants demonstrated that upp, not pyrR, encodes the quantitatively important uracil phosphoribosyltransferase activity. The pyrP gene probably encodes an integral membrane uracil permease.
authors.affiliation: Department of Biochemistry, University of Illinois, Urbana 61801.
authors.forename: R J
authors.initials: RJ
authors.lastname: Turner
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: R L
authors.initials: RL
authors.lastname: Switzer
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics*; D005809:Genes, Regulator / Q000235:genetics; D007763:Lac Operon; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D009690:Nucleic Acid Conformation; D033704:Nucleotide Transport Proteins; D016366:Open Reading Frames / Q000235:genetics; D010430:Pentosyltransferases / Q000096:biosynthesis / Q000235:genetics; D011743:Pyrimidines / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D029701:Saccharomyces cerevisiae Proteins; D013381:Subtilisins / Q000235:genetics; D013728:Terminator Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: C035528:FUR4 protein, S cerevisiae; D026901:Membrane Transport Proteins; D033704:Nucleotide Transport Proteins; D011743:Pyrimidines; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D010430:Pentosyltransferases; C023269:uracil phosphoribosyltransferase; D013381:Subtilisins