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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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- Spring '08