Arrows indicate the location of transcripts for the 1

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Unformatted text preview: encoded by the different versions of the MAT locus. Arrows indicate the location of transcripts for the 1, 2, and a1 genes at the MAT locus. indicates a blocked step. 9 such as pheromone. The 2 gene encodes a repressor of a-specific functions. Cells lacking a functional 2 gene product express both -specific and a-specific genes, and the simultaneous expression of both sets of genes is incompatible with mating. 1 2 double mutants mate like a cells because they fail to turn off a-specific functions and fail to turn on -specific functions. In effect, a simple network depending on two regulatory proteins—one an activator, the other a repressor—accounts for the a and cell types. In this network, 1 and 2 act as master regulatory genes whose products control the expression of a large number of genes required for the appropriate behavior of a or cells. What is the role and makeup of the MAT locus in an a cell? Mutant analyses of the MATa locus indicate that it has a slightly different configuration from that of the MAT locus (Fig. A.9b). No ste...
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