Distribution of retroviral integrations around transcription start sites. Distribution of the distance of MLV and HIV integration sites from the transcription start site (TSS) of targeted genes at 2500-bp (A), 50-bp (B), or 5-bp (C) resolution. The percentage of the total number of targeted genes (n) is plotted on the y-axis (A-B). The actual number of integrations is plotted on the y-axis (C). The black line (A) indicates the distribution of control random sites. A scheme of a classical core promoter engaged by the basal transcriptional machinery is shown in panel C (see Thomas and Chiang²⁰  for details and abbreviations), to visualize the apparent correlation between absence of MLV integration and promoter occupancy by the TFIID complex.