Genes regulating cell growth and proliferation are preferential targets of retroviral integration. (A) GO analysis of integration target genes in CD34⁺ cells. Genes identified as targets for RV (■) and LV (□) integration were analyzed for significant functional clusters with the DAVID 2.1 software. Functional categories are derived from the GO–Biological Process (establishment and/or maintenance of chromatin architecture, phosphorylation, transcription, signal transduction, apoptosis, cell cycle) and the GO–Molecular Function (GTPase regulator activity, protein serine/threonine kinase activity) classifications. Bars indicate the number of integration target genes annotated within the given category out of n genes eligible for each analysis. Asterisks denote the significance level of overrepresentation of any given category with respect to the human genome (▩), used as background population (***EASE score < .0005; **EASE score < .005; *EASE score < .05). The number of gene identifiers annotated within each functional category is indicated in the bars. (B) Functional clustering analysis comparing integration target and control gene lists. Function/disease categories were those significantly overrepresented in at least 1 integration target gene list (.005 < P < .05) using the Ingenuity Pathways Knowledge Base as background population and the Ingenuity analysis software. Bars represent the percentage of integration target genes belonging to each category among n genes eligible for the analysis. Asterisks denote the probability that differences observed between integration data sets (RV, LV, RV hot spots, and LV hot spots) and the control data set are due to chance alone (2-sample test for equality of proportions with continuity correction; ***P < .001; **P < .005; *P < .05). The number of genes annotated within each category is indicated in the bars.