PIC activity and integration site sequencing strategy. (A) PICs extracted from the cytoplasm (left panel) or nucleus (center panel) of mock-transduced (dark grey bars) or MxB-expressing cells (light grey bars) were assessed for in vitro integration activity. Percent infectivity, determined 48 h after infection (right panel), revealed the level of MxB restriction under these infection conditions. Results are the average of 4 independent experiments, with error bars denoting standard error of the mean. (B) Integration site sequencing strategy. In the representative HIV-1 provirus the viral DNA internal to the LTRs is a single bold line and the abutting cellular DNA is two thin lines (the region to be sequenced is in red). Thin blue lines, asymmetric DNA linker. The bold extensions of PCR primers denote elements required for Illumina sequencing. HIV-1 DNA harbors numerous MseI sites; only the relevant site downstream from the upstream U5 sequence is shown.