engleski

Chromatin Structure Remodeling and Activity of the Yeast PHO8 Promoter in Comparison to the PHO5 Promoter

The expression of the PHO5 and PHO8 genes, encoding a non-specific acid and alkaline phosphatase, respectively, is regulated in response to changes in the Pi concentration in medium by subsets of the same factors. However, despite of coordinative regulation of the two promoters, the PHO8 is almost 10 times weaker than the PHO5. Upon induction both promoters undergo strong remodeling of their chromatin structure, but the extent of remodeling at the PHO8 promoter is significantly lower then at the PHO5 (1). Here we show that, in contrast to the PHO5, only one of two Pho4 binding sites, previously mapped at the PHO8 promoter in vitro, is functional in vivo. Replacement of the inactive UASp1 element of PHO8, by the UASp1 element from the PHO5 promoter, resulted in more extensive remodeling of nucleosomes –3 and –2; at the same time, activity of the promoter variant increased ~2 fold. Deletion of the promoter region normally covered with nucleosomes –3 and –2 also resulted in 2 fold increase in promoter activity, supporting the correlation between promoter activity and the level of chromatin opening. These data altogether strongly suggest that the low level of PHO8 induction is at least in part due to inability of Pho4 to achieve complete chromatin remodeling at the PHO8 promoter through binding to the single site. There are also other features of the PHO8 promoter, which make it different from the PHO5. While PHO5 critically depends on Pho2 (2), the PHO8 promoter is only partially Pho2-dependent. Binding of Pho4 to the PHO8 promoter is Pho2-independent, but the presence of Pho2 increases promoter activity several folds. However, increase of the promoter activity in the presence of Pho2 is not accompanied with higher extent of chromatin remodeling. This shows that Pho2 directly increases activation potential of Pho4 rather then its ability to remodel chromatin.

ranscriptional regulation; chromatin; PHO5; PHO8; Saccharomyces cerevisiae

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