 D: Classification of primary response genes. For each gene, response time r is calculated as the sum of deduced transcriptional delay ∆t and mRNA half-life t1/2 and used for ranking. In general, immediate-early genes (IEGs) have short response times, whereas both immediate late genes (ILGs) and delayed early genes (DEGs) have longer response times. For ILGs, long response times are due to long mRNA half-lives. For DEGs, long response times are mainly due to long transcriptional delays (cf. boxplots). 