The effect of epigenetic modifications on HIV integration frequency in the ENCODE region. HIV integration sites and their matched random control sites were annotated using the indicated ENCODE tracks and then distributed into 10 bins based on the ENCODE annotation values. The expectation for random distribution is indicated by the horizontal line at one. For each annotation in A–D, both HIV-Avr (dark gray) and HIV-Mse (light gray) data sets achieved P < 10⁻⁶ for comparison to random distribution. ENCODE annotation: (A) H3 acetylation, (B) H3 K4 mono-methylation, (C) H4 acetylation, (D) H3 K27 tri-methylation, and (E) DNA CpG methylation (P < 0.0002).