Flexible zinc finger requirement for binding of the transcriptional activator Staf to U6 small nuclear RNA and tRNA(Sec) promoters

The transactivator Staf, which contains seven zinc finger motifs, exerts it s effect on gene expression by binding to specific targets in small nuclear RNA (snRNA) and snRNA-type gene promoters. In this work, binding site sele ction allowed us to identify the al-base pair ATTACCCATAATGCATYGCGG sequenc e as the high affinity consensus binding site for Staf. It shows a high seq uence divergence with Staf-responsive elements in the Xenopus selenocystein e tRNA (tRNA(Sec)) and human U6 snRNA promoters, By using a combination of approaches, we analyzed the interaction of wildtype and truncated Staf zinc finger domains with the consensus, Xenopus tRNA(Sec), and human U6 sites. Two main conclusions emerged from our data. First, the data clearly indicat e that zinc finger 7 does not establish base specific contacts in Staf-DNA complexes. The second conclusion concerns zinc finger 1, which is required for the binding to the Xenopus tRNA(Sec) site but is dispensable in the cas e of the human U6 site. Taking into account the sequence differences in the two sites, these findings demonstrate that Staf utilizes zinc finger 1 in a rather flexible manner, illustrating how a protein can interact with DNAs containing targets of different sequences.