Microbiology news and views
J. Mol. Micro. Biotechnol. 3: 287-293
SigB, SigC, and SigE from Myxococcus
xanthus Homologous to s32 are Not Required for Heat Shock Response but
for Multicellular Differentiation
Toshiyuki Ueki and Sumiko Inouye
Myxococcus xanthus has been known to have multiple sigma factors which are considered to play
important roles in regulation of gene expression in development. A new gene encoding a putative sigma factor,
sigE, was cloned by using a degenerate oligonucleotide corresponding to the conserved region 2.2 of
M. xanthus SigA. In the 2.0-kb nucleotide sequence, an open reading frame consisting of 280 amino acid residues was
identified. The amino acid sequence of SigE shows high similarity to heat shock sigma factors in bacteria. However,
the sigE gene is not induced by heat shock and deletion of
sigE does not affect production of heat shock
proteins. SigE is expressed during both vegetative growth and fruiting body development. In the deletion mutant of
the sigE gene fruiting body formation is initiated earlier and fewer spores are produced than in the parent
strain. Interestingly, the DsigE mutant shows defects in fruiting body formation at 37°C. In addition to SigE, SigB
and SigC show high sequence similarity to heat shock sigma factors. However, even if all three sigma factor
genes are disrupted, heat shock proteins are still normally induced. A
DsigBDsigCDsigE triple deletion strain
forms fruiting bodies earlier, but sporulats later than the parent strain. Spores from the triple deletion mutant
are aberrant and their viability is less than 0.001% compared with that of the parent strain, suggesting that
these sigma factors may have redundant functions in multicellular differentiation of
M. xanthus.
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