INTERACTION OF THE HUMAN T-CELL LYMPHOTROPHIC VIRUS TYPE-I (HTLV-I) TRANSCRIPTIONAL ACTIVATOR TAX WITH CELLULAR FACTORS THAT BIND SPECIFICALLY TO THE 21-BASE-PAIR REPEATS IN THE HTLV-I ENHANCER

The human T-cell lymphotrophic virus type I (HTLV-I) Tax protein activates transcription from three 21-base-pair (bp) repeat sequences in the viral enhancer. Using gel electrophoretic mobility-shift assays, we now show that Tax interacts directly with the nuclear proteins, Tax activation factors (TAFs), that bind the 21-bp repeats. This interaction is demonstrated by decreased electrophoretic mobilities of the TAFS-21-bp-repeats complexes upon supply of Tax exogenously. Formation of the TAFs-21-bp-repeats and Tax-TAFs-21-bp-repeats complexes correlates with in vivo transactivation by Tax. Furthermore, interaction of Tax with TAFs enhances their binding to the 21-bp repeats. These data indicate that trans-activation by Tax is most likely mediated by interaction of Tax with TAFs.