FIG. 5.

Transcriptional repression of CLN1 is required for full induction of the glucose-induced increase in minimum budding size. (A) The effect of glucose upon the CLN1 transcripts expressed from a CLN2p-CLN1 fusion (CLN1) and from a truncated CLN1 gene (cln1^tr) under control of its own promoter was analyzed in synchronized G₁ cells and plotted relative to cell volume as described in the legend to Fig. 3. Both forms of the CLN1 transcript were detected by Northern blot analysis with the CLN1 open reading frame as a probe. The budding index is plotted versus cell volume (bottom graph). Cells were grown in medium containing either glycerol-ethanol (○) or glucose (▪) as a carbon source. Primary data from Northern blot analysis of CLN1, cln1^tr, and ACT1 are presented at right. (B) Exchange of the CLN1 and CLN2 promoters reveals that transcriptional regulation is sufficient and, at least in part, necessary for the glucose-induced increase in budding size. Cell volume at budding was determined in strains carrying a single integrated copy of CLN2p-CLN1 or CLN1p-CLN2 at the CLN1 or CLN2 locus, respectively. Cells were either grown continuously on glycerol-ethanol or shifted to glucose. A representative experiment is presented for each strain. Data for the relevant CLN-deficient strains were either reproduced from Fig. 1 or determined as described for Fig. 1 and in Materials and Methods. The percent change in minimum budding size is presented.