Structural organization of Staf-DNA complexes

The transactivator Staf, which contains seven contiguous zinc fingers of th e C-2-H-2 type, exerts its effects on gene expression by binding to specifi c targets in vertebrate small nuclear RNA (snRNA) and snRNA-type gene promo ters. Here, we have investigated the interaction of the Staf zinc finger do main with the optimal Xenopus selenocysteine tRNA (xtRNA(Sec)) and human U6 snRNA (hU6) Staf motifs, Generation of a series of polypeptides containing increasing numbers of Staf zinc fingers tested in binding assays, by inter ference techniques and by binding site selection served to elucidate the mo de of interaction between the zinc fingers and the Staf motifs, Our results provide strong evidence that zinc fingers 3-6 represent the minimal zinc f inger region for high affinity binding to Staf motifs, Furthermore, we show that the binding of Staf is achieved through a broad spectrum of close con tacts between zinc fingers 1-6 and xtRNA(Sec) or optimal sites or between z inc fingers 3-6 and the hU6 site, Extensive DNA major groove contacts contr ibute to the interaction with Staf that associates more closely with the no n-template than with the template strand. Based on these findings and the s tructural information provided by the solved structures of other zinc finge r-DNA complexes, we propose a model for the interaction between Staf zinc f ingers and the xtRNA(Sec), Optimal and hU6 sites.