, Volume 28, Issue 1, pp 1-11

Functional analysis of the ABF1-binding sites within the Ya regions of the MATa and HMRa loci of Saccharomyces cerevisiae

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Cell type in the yeast Saccharomyces cerevisiae is determined by information present at the MAT locus. Cells can switch mating types when cell-type information located at a silent locus, HML or HMR, is transposed to the MAT locus. The HML and HMR loci are kept silent through the action of a number of proteins, one of which is the DNA-binding protein, ABF1. We have identified a binding site for ABF1 within the Ya region of MAT a and HMR a. In order to examine the function of this ABF1-binding site, we have constructed strains that lack the site in the MAT a or HMR a loci. Consistent with the idea that ABF1 plays a redundant role in silencing, it was found that a triple deletion of the ABF1-binding sites at HMRE, Ya and I did not permit the expresion of HMR a. We have also shown that chromosomal deletion of the binding site at MATY a had no effect on the level of cutting by the HO endonuclease nor on the amount of mating-type switching observed. Similarly, chromosomal deletion of all three ABF1-binding sites at HMR a had no effect on the directionality of mating-type switching.

Communicated by R. J. Rothstein