STAT5Δ binds to the HIV-1 LTR in living U1 cells. (A) Identification of 2 putative STAT binding sites (STAT A and STAT B) in the U3 region of the HIV-1 LTR according to TFSEARCH software (see “Materials and methods”). (B) Positions of primers and TaqMan probes selected to amplify 2 regions in the LTR promoter represented with regard to the transcription start site (+1) and encompassing the putative STAT5 binding sites. The numbers below the investigated segments indicate the location of the 5′ primer used for amplification. For each analyzed region, the amounts of chromatin immunoprecipitated after 1 hour of GM-CSF stimulation vs. unstimulated cells by polyclonal Ab against STAT5-N (C) or STAT5-C (D) are shown. The percentage of input chromatin for the 2 LTR regions indicated in panel B was normalized to that of the unrelated genomic region B13. The results are expressed as fold enrichment over B13-related levels. These results were obtained in a single experiment representative of two independently performed. Real-time PCR (TaqMan) was performed in triplicate in each experiment (mean ± standard deviation).