Two Distinct Domains in Staf To Selectively Activate Small Nuclear RNA-Type and mRNA Promoters

Abstract

Staf is a transcriptional activator of prime importance for enhanced transcription of small nuclear (snRNA) and snRNA-type genes transcribed by RNA polymerases II and III (Pol II and III). In addition to this activity, it also possesses the capacity to stimulate expression from an RNA polymerase II mRNA promoter. This promiscuous activator thus provides a useful model system for studying the mechanism by which one single transcription factor can activate a large variety of promoters. Here, we report the use of in vivo assays to identify the Staf activation domains involved in promoter selectivity. Analysis of Staf mutants reveals the existence of two physically and functionally distinct regions, outside of the DNA binding domain, responsible for mediating selective transcriptional activation. While a 93-amino-acid domain, with the striking presence of four repeated units, is specialized for transcriptional activation of an mRNA promoter, a segment of only 18 amino acids, with a critical Leu-213 residue, acts specifically on Pol II and Pol III snRNA and snRNA-type promoters. In addition, this study disclosed the fundamental importance of invariant leucine and aspartic acid residues located in each repeat unit of the mRNA activation domain. Staf is therefore the first transcriptional activator described so far to harbor two physically and functionally distinct activator domains. This finding suggests that the same activator can contact different, specialized transcription complexes formed on different types of basal promoters through promoter-specific transactivation pathways.Transcriptional activation in eukaryotes is achieved by regulatory proteins recruiting the transcriptional machinery and chromatin remodeling factors to the promoter. Transcriptional activators have been shown to present a modular organization consisting of distinct domains for sequence-specific DNA binding and transcriptional activation through interaction with other proteins (for a review, see reference 34). DNA binding domains of many transactivators fall into readily identifiable classes. Instead, domains responsible for transcriptional activity may not possess such a well-defined organization. While no obvious sequence similarity has been detected among the activation domains of diverse activator proteins, they nevertheless often carry a distinctive amino acid composition. For example, activation domains particularly rich either in prolines, glutamines, acidic amino acids, or hydroxylated amino acids have been described (for reviews, see references 4, 21, 27, and 51). Despite the identification of targets for numerous activation domains and elucidation of the functional importance of particular residues, the structural basis for the capacity of an activation domain to stimulate transcription remains poorly understood. However, recent structural studies suggest that the ␣-helix may be a common structural motif in the binding of transactivation factors to transcriptional activation factors (22,52). Transcriptional activators were also desc...

CHD8 Associates with Human Staf and Contributes to Efficient U6 RNA Polymerase III Transcription

“…As observed before (45), the addition of purified recombinant hStaf to a HeLa cell extract also activated U6 transcription from a naked DNA template in an SPH sequence-dependent manner, although in our hands, this activation was rather weak (lanes 5 to 8). Thus, like many transcription factors, including chimeric proteins containing the VP16 activation domain (see, for example, reference 37), hStaf can activate transcription from both naked (45) (51). The activation domain contains a region required for activation of snRNA-type genes and another region composed of four imperfect tandem repeats required for the activation of mRNA-encoding Pol II genes (51).…”

“…Thus, like many transcription factors, including chimeric proteins containing the VP16 activation domain (see, for example, reference 37), hStaf can activate transcription from both naked (45) (51). The activation domain contains a region required for activation of snRNA-type genes and another region composed of four imperfect tandem repeats required for the activation of mRNA-encoding Pol II genes (51). The zinc finger domain contains seven zinc fingers of the C 2 -H 2 type, different sets of which can be used to bind to different DNA targets (49).…”

Zfp143 Regulates Nanog Through Modulation of Oct4 Binding

“…Zfp143, also known as STAF, is a zinc finger protein that was first identified as a transcription activator of small nuclear RNA (snRNA) and snRNA-type genes transcribed by RNA polymerase II and III [28 -30] with seven-zinc finger repeats for DNA binding in the middle and two transactivation domains at the amino-terminal portion [29]. Zfp143 also plays a key role in basal and tissue-specific expression of transaldolase and regulating the metabolic network controlling cell survival and differentiation [31].…”

Small Nuclear RNA Genes: a Model System to Study Fundamental Mechanisms of Transcription

“…37, and references therein). Xenopus Staf contains two separable activation domains capable of selectively stimulating transcription from snRNA-and mRNA-type promoters (38). The human proteins ZNF143 and, to a lesser extent, ZNF76 are similar to Xenopus Staf, share similar DNA binding specificities, and can activate pol II and III snRNA gene transcription (35,36).…”