Figure 3. Expression of cell cycle-regulated genes. The expression of approximately 700 cell cycle-regulated genes (Spellman et al, 1998) was analyzed by hierarchical clustering, as described in Materials and Methods. The genes were divided into five classes defined by Spellman et al. (M/G1,G1, S, G2/M, and M), reflecting the cell cycle phase during which those transcript levels peak in cycling cells. Each class of genes was clustered separately using data recovered from a total of 86 microarrays. For this display, data are shown for wild-type and mec1 cells responding to MMS treatment and ionizing radiation (IR) (this study) and cells progressing through the cell cycle after alpha factor synchronization (Spellman, et al. 1998). The timepoints represented for the DNA damage responses are 5, 15, 30, 45, 60, 90, and 120 minutes after the MMS treatment and at 5, 10, 20, 30, 45, 60, 90, and 120 minutes after ionizing radiation. Changes in transcript levels are represented using the color scale indicated at the bottom right of the figure.