engleski

Important, distinctive role of the RSC complex in chromatin structure remodelling at the yeast PHO promoters

The massive transition of chromatin structure at the yeast PHO5 promoter from a repressed to an active, open state was clearly demonstrated to be a prerequisite for promoter activation. We have previously shown that out of 15 non-essential chromatin-remodelling ATPases examined, chromatin structure remodelling at the PHO5 promoter involved the SWI/SNF and Ino80 remodelling complexes. In the absence of either SWI/SNF or Ino80 complex, chromatin opening kinetics were strongly delayed and by simultaneous inactivation of both complexes synthetic effect was observed, but eventually complete opening was accomplished. Therefore no remodelling complex critically required for PHO5 promoter opening has been identified yet. The RSC complex is essential, the most abundant chromatin-remodelling complex in yeast and has been shown to disassemble nucleosomes in vitro. As inactivation of the RSC ATPase subunit Sth1 is lethal, we have used a temperature sensitive sth1td mutant to assess the possible effect of RSC inactivation on the PHO5 chromatin remodelling. The rate of chromatin opening and the consequent activation of the PHO5 promoter upon physiological induction in phosphate-free medium were significantly delayed by Sth1 depletion and this effect was even more pronounced under weaker induction conditions. Chromatin remodelling and consequent activation of a Gal4-activated PHO5 promoter variant, induced through GAL-signalling pathway, was similarly affected by RSC inactivation showing that the observed effect was independent of the induction conditions and transactivator involved. However, simultaneous inactivation of SWI/SNF and RSC complexes completely prevented remodelling of the native PHO5 promoter, as well as the promoter variant, showing a functional interplay of the two complexes in the remodelling process. Also, inactivation of the RSC complex in the isw1 chd1 double mutant, which by itself showed a significant delay in the kinetics of PHO5 chromatin remodelling, completely abolished remodelling. Altogether these results pointed out a crucial, distinctive role of the RSC complex for the remodelling process in the absence of dedicated remodellers like SWI/SNF, Isw1 and Chd1. Interestingly, inactivation of the RSC complex had no significant effect on chromatin remodelling at the other two PHO promoters, PHO8 and PHO84, which are coactivated with PHO5.

RSC cmplex; chromatin remodelling; yeast PHO promoters

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