| Research Abstract |
The genome sequence of the unicellular cyanobacterium Synechocystis sp. PCC 6803 was deteremined by Kazusa DNA Institute several years ago, and the presence of four group 2 sigma factors (SigB, SigC, SigD and SigF) has been clarified. Since each of these sigrna factors are well conserved among divergent cyanobacteria, respective function for each sigma appears to be well established in cyanobacteria. In this study, we first studied the in vitro specificity of group 2 sigma factors, and found that group 1 and group 2 sigma factors are sigma factors sharing similar promoter recognition specificity. We then performed expression analysis of these sigma factors, and found that :
1. The sigB gene product is induced by heat shock.
2. The sigC function is activated during the stationary growth phase.
3. The sigD expression is enhanced by various stresses such as, low temperature, salt, high osmotic pressure and high light, dependent on a two-component histidinc kinase, Hik33.
4. The sigE expression is largely dependent on the global nitrogen regulator, NtcA, which is activated by depletion of nitrogen sources. We have also found that NtcA-dependent transcription is activated by 2-oxoglutarate in vitro.
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