To define the contribution of CDK8 versus CDK19 to gene expression control, we performed a series of microarray assays for cells where each kinase was stably knocked down. Toward this end, we subjected HCT116 cells to three different stress stimuli: 5-fluorouracil (5FU), glucose deprivation, and hypoxia. We found that CDK8, but not CDK19, functions as a widespread coactivator of HIF1A target genes in hypoxia. Total RNA from HCT116 cells harvested using an RNeasy kit (Qiagen) was used for gene expression analysis on Affymetrix HuGene 1.0 ST arrays following the manufacturer’s instructions. Differential gene expression was determined with Partek software using one-way ANOVA.