FIG. 5.

Model for the role of Snf1 kinase in coordinating glucose and acetate controls on early and late phases of meiotic differentiation. Negative regulation is represented by perpendicular lines, and positive regulation is indicated by arrows; broken arrows indicate that activation is not fully dependent on the upstream signal. X, unidentified regulatory gene(s). Meiosis is controlled by at least three different signaling pathways: (i) growth—in growing cells, IME1 transcript levels are fully repressed; (ii) acetate—acetate or other nonfermentable carbon sources increase IME1 and IME2 transcript levels, leading to early meiotic events, such as DNA replication and recombination; acetate separately activates late meiotic events (chromosome segregation and spore formation); and both early regulation and late regulation by acetate requires Snf1 kinase; (iii) glucose—glucose represses meiosis at both early and late stages by repressing Snf1 kinase activity. Other nutritional controls on meiosis, in addition to the ones shown on the diagram, are also possible. Chrom. Seg., chromosome segregation; Form., formation.