cbk1 and swi5 mutations have an additive effect on EGT2 expression. (A) S1 nuclease protection assays were performed using probes specific for EGT2, SCW11, and CMD1 (internal control). RNAs were prepared from the following strains: DY2396 (bud4), DY9197 (BUD4), DY3923 (bud4 ace2), DY9190 (BUD4 ace2), DY3925 (bud4 swi5), DY9194 (BUD4 swi5), DY4653 (bud4 ace2 swi5), DY9186 (BUD4 ace2 swi5), DY5794 (bud4 cbk1), DY9195 (BUD4 cbk1), DY5796 (bud4 ace2 cbk1), DY9188 (BUD4 ace2 cbk1), DY5798 (bud4 swi5 cbk1), DY9192 (BUD4 swi5 cbk1), DY5800 (bud4 ace2 swi5 cbk1), and DY9184 (BUD4 ace2 swi5 cbk1). (B) mRNA levels were determined by PhosphorImager for EGT2 and SCW11 (from the data in panel A) and for DSE2 and CTS1 (data not shown). mRNA values are normalized to the wild-type strain. For this experiment, results are only shown for bud4 strains, but similar results were seen with BUD4 strains. (C) EGT2 activation requires either Swi5 or both Ace2 and Cbk1, while SCW11, DSE2, and CTS1 expression requires both Ace2 and Cbk1 but not Swi5.