Depletion of Abp1 protein in the triple deletion Δabp1 Δcbh1 Δcbh2 int. nmt81-abp1+ mutant strain leads to cell cycle arrest. Phase contrast microscopy shows cells to be highly elongated 24–36 hrs following addition of 10 μg/μl thiamine (to repress transcription of the abp1+ gene) indicating that cell cycle progression is blocked. Cells also show other morphological defects including multi-septation and branching. Left panel: Control (no thiamine). Right panel: Cells after 24 hours of thiamine treatment.