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Journal of Bacteriology, October 2001, p. 5513-5522, Vol. 183, No. 19
Department of Biochemistry, University of
Illinois, Urbana, Illinois 61801
Received 12 April 2001/Accepted 5 July 2001
The B. subtilis pyrG gene, which encodes CTP
synthetase, is located far from the pyrimidine biosynthetic operon on
the chromosome and is independently regulated. The pyrG
promoter and 5' leader were fused to lacZ and integrated
into the chromosomes of several B. subtilis strains
having mutations in genes of pyrimidine biosynthesis and
salvage. These mutations allowed the intracellular pools of cytidine
and uridine nucleotides to be manipulated by the composition of the
growth medium. These experiments indicated that pyrG
expression is repressed by cytidine nucleotides but is largely
independent of uridine nucleotides. The start of
pyrG transcription was mapped by primer extension
to a position 178 nucleotides upstream of the translation initiation
codon. A factor-independent termination hairpin lying between the
pyrG promoter and its coding region is
essential for regulation of pyrG expression.
Primer-extended transcripts were equally abundant in repressed and
derepressed cells when the primer bound upstream of the terminator, but
they were much less abundant in repressed cells when the primer bound downstream of the terminator. Furthermore, deletion of the terminator from pyrG-lacZ fusions integrated into the chromosome
yielded elevated levels of expression that was not repressible by
cytidine. We suggest that cytidine repression of pyrG
expression is mediated by an antitermination mechanism in which
antitermination by a putative trans-acting protein is
reduced by elevated levels of cytidine nucleotides. Conservation of
sequences and secondary structural elements in the pyrG
5' leaders of several other gram-positive bacteria indicates that their
pyrG genes are regulated by a similar mechanism.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5513-5522.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Regulation of Transcription of the Bacillus
subtilis pyrG Gene, Encoding Cytidine Triphosphate
Synthetase
*
Corresponding author. Mailing address: Department of
Biochemistry, University of Illinois, 600 South Mathews Ave., Urbana, IL 61801. Phone: (217) 333-3940. Fax: (217) 244-5858. E-mail: rswitzer{at}uiuc.edu.
Journal of Bacteriology, October 2001, p. 5513-5522, Vol. 183, No. 19
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5513-5522.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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