Figure 4. Expression of cell-cycle genes that correlated with cell cycle arrest. Hierarchical clustering analysis of all 700 cell-cycle genes, as described in Materials and Methods, revealed three clusters of genes whose transcript levels seemed to correlate with the cell cycle arrest point induced by MMS and ionizing radiation (IR). The timepoints represented for the DNA damage responses are the same described in Figure 3. Genes that are known to regulate cell cycle progression are labeled in purple. The color scale used to represent variations in transcript abundance is shown in the key at the bottom right of the figure.