A, B The plb1Δ mutant exhibits a cold-sensitive defect in nutrient-dependent mating repression. A Wild type (left) and plb1Δ (right) cells were streaked onto YEAU, and incubated at 20°C for 5 days prior to photographing a group of isolated colonies of each culture. B Photomicrographs of cells from the cultures shown in A. The plb1Δ culture (right panel) exhibited very high mating activity, as indicated by the high frequency of zygotes (e.g., note the cell marked by the white arrowhead) and asci (e.g., note the cell indicated by the black arrowhead). Zygotes and asci were relatively rare in the wild-type culture (left panel)