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J. Bacteriol., Feb 1997, 1153-1164, Vol 179, No. 4
G Homuth, S Masuda, A Mogk, Y Kobayashi and W Schumann
In 1992, we described the cloning and sequencing of the dnaK locus of
Bacillus subtilis which, together with transcriptional studies, implied a
tetracistronic structure of the operon consisting of the genes hrcA, grpE,
dnaK, and dnaJ. We have repeated the Northern blot analysis, this time
using riboprobes instead of oligonucleotides, and have detected a
heat-inducible 8-kb transcript, suggesting the existence of additional heat
shock genes downstream of dnaJ. Cloning and sequencing of that region
revealed the existence of three novel heat shock genes named orf35, orf28,
and orf50, extending the tetra- into a heptacistronic operon. This is now
the largest dnaK operon to be described to date. The three new genes are
transcribed as a part of the entire dnaK operon (8.0-kb heptacistronic
heat-inducible transcript) and as part of a suboperon starting at an
internal vegetative promoter immediately upstream of dnaJ (4.3-kb
tetracistronic non-heat-inducible transcript). In addition, the Northern
blot analysis detected several processing products of these two primary
transcripts. To demonstrate the existence of the internal promoter, a DNA
fragment containing this putative promoter structure was inserted upstream
of a promoterless bgaB gene, resulting in the synthesis of
beta-galactosidase. Challenging this transcriptional fusion with various
stress factors did not result in the activation of this promoter. To assign
a biological function to the three novel genes, they have each been
inactivated by the insertion of a cat cassette. All of the mutants were
viable, and furthermore, these genes are (i) not essential for growth at
high temperatures, (ii) not involved in the regulation of the heat shock
response, and (iii) sporulation proficient. Blocking transcription of the
suboperon from the upstream heat-inducible promoter did not impair growth
and viability at high temperatures.
Copyright © 1997, American Society for Microbiology
The dnaK operon of Bacillus subtilis is heptacistronic
Institute of Genetics, University of Bayreuth, Germany.
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