Differential remodeling of the HIV-1 nucleosome upon transcription activators and SWI/SNF complex binding

Here we have examined HIV-1 nucleosome remodeling upon the binding of transcription factors and the SWI/SNF complex using a novel approach. The approach combines UV laser protein-DNA crosslinking, electrophoretic mobility-shift analysis and DNase I protection analysis with immunochemical techniques. It was found that single activator-bound HIV-1 nucleosomes exhibit very weak perturbation in histone NH2 tail-DNA interactions. However, the simultaneous binding of the transcription activators Sp1, NF-kB1, LEF-1 and USF synergistically increased the release of histone NH2 tails from nucleosomal DNA. In contrast, the binding of SWI/SNF complex to HIV-1 nucleosome disrupted structured histone domain-DNA contacts, but not histone NH2 tail-DNA interactions. Stable remodeled nucleosomes, (obtained after detachment of SWI/SNF), displayed identical structural alterations with those bound to SWI/SNF. These results demonstrate a different in vitro remodeling of the HIV-1 nucleosome upon the binding of multiple transcription activators and of SWI/SNF complex.