Previous Article | Next Article ![]()
J. Bacteriol., Oct 1996, 5719-5731, Vol 178, No. 19
HC Tsui, G Feng and ME Winkler
The amiB-mutL-miaA-hfq-hflX-hflK-hflC superoperon of Escherichia coli
contains genes that are important for diverse cellular functions, including
DNA mismatch repair (mutL), tRNA modification (miaA), pleiotropic
regulation (hfq), and proteolysis (hflX-hflK-hflC). We show that this
superoperon contains three E simga(32)-dependent heat shock promoters,
P(mutL)HS,P(miaA)HS, and P1(hfq)HS, in addition to four E
sigma(70)-dependent promoters, P(mutL), P(miaA), P2(hfq), and P3(hfq).
Transcripts from P(mutL)HS and P(miaA)HS were most prominent in vivo during
extreme heat shock (50 degrees C), whereas P1(hfq)HS transcripts were
detectable under nonshock conditions and increased significantly after heat
shock at 50 degrees C. The P(mutL)HS, P(miaA)HS, and P1(hfq)HS transcripts
were not detected in an rpoH null mutant. All three promoters were
transcribed by E sigma (32) in vitro at 37 degrees C and contain -35 and
-10 regions that resemble the E sigma(32) consensus. In experiments to
assess the possible physiological relevance of the P(mutL)HS and P(miaA)HS
promoters, we found that E. coli prototrophic strain MG 1655 increased in
cell mass and remained nearly 100% viable for several hours at 50 degrees C
in enriched media. In these cells, a significant fraction of mutL and
hfq-hflA region transcripts were from P(mutL)HS and P1(hfq)HS,
respectively, and the amounts of the miaA, hfq, hflX, hflK, and hflC
transcripts increased in comparison with those in nonstressed cells. The
cellular amounts of MutL and the hfq gene product (HF-I protein) were
maintained during heat shock at 44 or 50 degrees C. Consistent with their
expression patterns, miaA and hfq were essential for growth and viability,
respectively, at temperatures of 45 degrees C and above. Together, these
results suggest that there is a class of E sigma(32) promoters that
functions mainly at high temperatures to ensure E. coli function and
survival.
Copyright © 1996, American Society for Microbiology
Transcription of the mutL repair, miaA tRNA modification, hfq pleiotropic regulator, and hflA region protease genes of Escherichia coli K-12 from clustered Esigma32-specific promoters during heat shock
Department of Microbiology and Molecular Genetics, University of Texas-- Houston Medical School, 77030-1501, USA.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»