HIV-1 Tat directly binds to NFkappaB enhancer sequence: role in viral and cellular gene expression.

HIV-1 Tat protein reprograms cellular gene expression of infected as well as uninfected cells apart from its primary function of transactivating HIV-1 long terminal repeat (LTR) promoter by binding to a nascent RNA stem-loop structure known as the transactivator response region (TAR). Tat also induces chromatin remodeling of proviral LTR-mediated gene expression by recruiting histone acetyl transferases to the chromatin, which results in histone acetylation. Furthermore several studies have shown convincing evidence that Tat can transactivate HIV-1 gene expression in the absence of TAR, the molecular mechanism of which remains to be elucidated. Here we show a direct interaction of Tat with nuclear factor kappa B (NFkappaB) enhancer, a global regulatory sequence for many cellular genes both in vitro and in vivo. This interaction not only provides a novel molecular basis to explain TAR-independent transactivation in HIV-1, but also points toward the potential mechanism of Tat- mediated modulation of cellular genes.