K-means clustering of 819 differentially expressed genes. Gene expression levels were calculated using MAS, RMA, and dChip, then normalized using the associated algorithms. Genes with a raw expression level below 150 were excluded. Genes with more than 4-fold change in expression compared to baseline (0 hours) were selected. Only those genes selected irrespective of normalization method were further analyzed. Eleven clusters were identified by the “K-means best” algorithm and 3 pairs of clusters (1a and b, 2a and b, and 3a and b) were merged due to their similar patterns.