Figure 1.

Exocytosis is inhibited in late G₁ phase. A, conditional cdc34-2 mutants exhibit Bgl2 secretion defects at the restrictive temperature. Internal (“In”) and external (“Ex”) pools of Bgl2 in WT, cdc34-2 (late G₁ phase), and cdc53-1 (late G₁ phase) cells were examined by Western blot analysis. Cells were grown at 25 °C or shifted to 37 °C for 2 h. Alcohol dehydrogenase (Adh1) levels were probed as a protein loading control. The conditional mutants and cell cycle arrest points are listed to the right. B, quantification of Bgl2 accumulation in A. n = 3. *, p < 0.01. C, Cdk1 is required for the reduction in Bgl2 secretion in metaphase-arrested cdc34-2 cells. cdc34-2 and cdc34-2 cdk1-as1 cells were grown to early log phase at 25 °C and shifted to 37 °C for 1.5 h. Cells were then treated with DMSO (mock) or 15 μm 1NM-PP1 for 30 min. Internal and external pools of Bgl2 in cdc34-2 and cdc34-2 cdk1-as1 cells were examined by Western blotting. Corresponding immunoblots of alcohol dehydrogenase serve as a protein loading control. D, quantification of Bgl2 accumulation in C. n = 3; *, p < 0.01. E, invertase secretion was not changed in cdc34-2 and cdc28-4 mutants. Cells were grown at 25 °C or shifted to 37 °C for 1.5 h, and secretion of invertase was examined. The percentage of external invertase (secreted) versus total invertase was measured. Error bars represent S.D. (n = 3). AU, arbitrary unit.