Recruitment of the Swi/Snf complex by Ste12-Tec1 promotes Flo8-Mss11-mediated activation of STA1 expression.

In the yeast Saccharomyces diastaticus, expression of the STA1 gene, which encodes an extracellular glucoamylase, is activated by the specific DNA-binding activators Flo8, Mss11, Ste12, and Tec1 and the Swi/Snf chromatin-remodeling complex. Here we show that Flo8 interacts physically and functionally with Mss11. Flo8 and Mss11 bind cooperatively to the inverted repeat sequence TTTGC-n-GCAAA (n = 97) in UAS1-2 of the STA1 promoter. In addition, Flo8 and Mss11 bind indirectly to UAS2-1 of the STA1 promoter by interacting with Ste12 and Tec1, which bind to the filamentation and invasion response element (FRE) in UAS2-1. Furthermore, our findings indicate that the Ste12, Tec1, Flo8, and Mss11 activators and the Swi/Snf complex bind sequentially to the STA1 promoter, as follows: Ste12 and Tec1 bind first to the FRE, whereby they recruit the Swi/Snf complex to the STA1 promoter. Next, the Swi/Snf complex enhances Flo8 and Mss11 binding to UAS1-2. In the final step, Flo8 and Mss11 directly promote association of RNA polymerase II with the STA1 promoter to activate STA1 expression. In the absence of glucose, the levels of Flo8 and Tec1 are greatly increased, whereas the abundances of two repressors, Nrg1 and Sfl1, are reduced, suggesting that the balance of transcriptional regulators may be important for determining activation or repression of STA1 expression.