The transcriptional wiring diagram of the budding yeast cell cycle. (a) Waves of transcriptional activation (red) and repression (green) across two synchronous division cycles, as determined by DNA microarray analysis. Colored bars indicate cell cycle phases. (b) Cell-cycle-regulated gene clusters. (c) The main transcriptional circuits. The dashed line represents undetermined intermediaries between the CLN2 cluster and the CLB2 cluster. Panels (a) and (b) are modified and reproduced with permission from the experiment depicted in Figure 1 of Spellman et al. .