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Journal of Bacteriology, January 2001, p. 221-228, Vol. 183, No. 1
Department of Microbiology, University of
Alabama at Birmingham, Birmingham, Alabama 35294
Received 8 May 2000/Accepted 11 October 2000
In Escherichia coli, pyrimidine-mediated regulation of
upp expression occurs by UTP-sensitive selection of
alternative transcriptional start sites, which produces transcripts
that differ in the ability to be elongated. The upp
initially transcribed region contains the sequence GATTTTTTTTG
(nontemplate strand). Initiation can occur at either the first or
the second base in this sequence (designated G6 and A7, with numbering
from the promoter
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.221-228.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
A Long T · A Tract in the upp
Initially Transcribed Region Is Required for Regulation of
upp Expression by UTP-Dependent Reiterative Transcription in
Escherichia coli
10 region). High intracellular UTP levels favor
initiation at position A7; however, the resulting transcripts are
subject to reiterative transcription (i.e., repetitive UMP addition)
within the 8-bp T · A tract in the initially transcribed region
and are aborted. In contrast, low intracellular UTP levels favor
initiation at position G6, which results in transcripts that can, in
part, avoid reiterative transcription and be elongated normally. In
this study, we examined the regulatory requirement for the long T
· A tract in the upp initially transcribed region. We
constructed upp promoter mutations that shorten the T
· A tract to 7, 6, 5, 4, 3, or 2 bp and examined the effects of these
mutations on upp expression and regulation. The results
indicate that pyrimidine-mediated regulation is gradually reduced as
the T · A tract is shortened from 7 to 3 bp; at which point
regulation ceases. This reduction in regulation is due to
large-percentage increases in upp expression in cells grown
under conditions of pyrimidine excess. Quantitation of cellular
transcripts and in vitro transcription studies indicate that the
observed effects of a shortened T · A tract on upp
expression and regulation are due to increases in the fraction of both
G6- and A7-initiated transcripts that avoid reiterative transcription and are elongated normally.
*
Corresponding author. Mailing address: UAB Department
of Microbiology, BBRB 409, 1530 3rd Ave. S., Birmingham AL 35294-2170. Phone: (205) 934-6289. Fax: (205) 975-5479. E-mail:
ChuckT{at}uab.edu.
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