The activities of the other σH-dependent promoters preceding sigN (PN1) and rpp operon (Prpp), which are also known for their dependence on σH (Takano et al., 2007),
were also significantly downregulated in the bldG mutant (Fig. 3a). These observations supported the hypothesis that BldG regulates the activity of σH and alternative sigma factors by binding to RshA. Further, the σH-dependent transcription was studied by an in vitro transcription assay (Fig. 3b). As described in previous studies, RshA inhibited the σH-dependent transcription at PH1. This RshA-dependent transcriptional repression was abolished in a dose-dependent manner by the addition of BldG at excess molar ratios (Fig. 3b). This finding can be attributed to the dissociation of σH from RshA, which in turn
binds to BldG. The lines of evidence obtained in this study suggest that the role of BldG is highly GDC-0980 pleiotropic. BldG regulates the expression of both developmental and stress-responsive genes in S. griseus. Since σH and its paralogs are not essential for the initiation of development (Takano et al., 2007), BldG probably binds to another sigma-factor antagonist involved in the developmental control. Recently, Parashar et al. (2009) reported that BldG binds Akt inhibitor ic50 to the putative anti-sigma factor encoded by SCO3548, the adjacent cds, to control the key developmental processes in S. coelicolor A3(2). The specific sigma factor regulated by this anti-sigma factor is expected to be involved in developmental control, although this sigma factor has not yet been identified. The conserved gene organization suggests that these findings would also be observed in S. griseus. During the writing of this
paper, Sevcikova et al. (2010) reported a similar observation on the interaction between BldG and RshA in S. coelicolor A3(2). The authors demonstrated specific interaction between BldG and UshX (the RshA ortholog) by pull-down and two-hybrid analyses and showed that the activity of the σH-dependent promoter preceding ushX-sigH operon (sigHp2; equivalent of PH1 of S. griseus) is abolished in a bldG mutant of S. coelicolor. Overall, our results are confirmatory except that the activities of the σH-independent promoters preceding rshA (PH2 and PH3) were reduced in the bldG mutant of S. griseus (Fig. 3a). In contrast, the corresponding promoters Ketotifen of S. coelicolor (sigHp3 and sigHp4) were upregulated in the bldG mutant of S. coelicolor A3(2) (Sevcikova et al., 2010). Currently, we do not know why the σH-independent promoters were also affected by the knockout of bldG, but the difference in the two species implies that this is due to some indirect effect. On the other hand, the identical evidence regarding σH-dependent promoters obtained in the two phylogenetically divergent species strongly suggests that the regulation generally occurs in this group of organisms. Similarly as in S.