Haploid strains carrying mata mutations mate normally

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Unformatted text preview: rility-producing mutations have been isolated that map at the MATa locus. Haploid strains carrying MATa mutations mate normally and fall into a single complementation group known as a1. The lack of any detectable haploid phenotype for MATa mutations suggests that the a1 protein performs no function necessary for mating or differentiation into a cells. It is the lack of 1 and 2 functions that makes a cells what they are. a cells do not express -specific functions because they lack the 1 activator, and they constitutively express a-specific functions because they lack the 2 repressor. In short, the a cell type arises through a default pathway requiring no action on the part of the MAT-encoded regulatory proteins. What happens in a MATa/ MAT heterozygous diploid? According to the model (Fig. A.9c), the a1 and 2 regulators act in concert to perform a series of negative functions. The a1- 2 coregulators, acting together, repress expression of 1; as a result, the -specific genes (or sg genes) are not activated. The a1- 2 coregulators also repress expression of haploid-specific genes (hsg genes) that normal...
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