The Large Subunit of Basal Transcription Factor SNAP_c Is a Myb Domain Protein That Interacts with Oct-1

Abstract

The human RNA polymerase II and III snRNA promoters have similar enhancers, the distal sequence elements (DSEs), and similar basal promoter elements, the proximal sequence elements (PSEs). The DSE, which contains an octamer motif, binds broadly expressed activator Oct-1. The PSE binds a multiprotein complex referred to as SNAP c or PTF. On DNAs containing both an octamer site and a PSE, Oct-1 and SNAP c bind cooperatively. SNAP c consists of at least four stably associated subunits, SNAP43, SNAP45, SNAP50, and SNAP190. None of the three small subunits, which have all been cloned, can bind to the PSE on their own. Here we report the isolation of cDNAs corresponding to the largest subunit of SNAP c , SNAP190. SNAP190 contains an unusual Myb DNA binding domain consisting of four complete repeats (Ra to Rd) and a half repeat (Rh). A truncated protein consisting of the last two SNAP190 Myb repeats, Rc and Rd, can bind to the PSE, suggesting that the SNAP190 Myb domain contributes to recognition of the PSE by the SNAP complex. SNAP190 is required for snRNA gene transcription by both RNA polymerases II and III and interacts with SNAP45. In addition, SNAP190 interacts with Oct-1. Together, these results suggest that the largest subunit of the SNAP complex is involved in direct recognition of the PSE and is a target for the Oct-1 activator. They also provide an example of a basal transcription factor containing a Myb DNA binding domain.The regulation of transcription initiation is mediated by the interplay between two classes of promoter elements: the basal promoter elements, which can be defined as those promoter elements sufficient to direct basal levels of transcription in vitro, and the regulatory elements, which modulate the levels of transcription. The basal elements are recognized by basal transcription factors, whereas the regulatory elements are recognized by either transcriptional activators or repressors. Eucaryotic activators are often modular, consisting of a DNA binding domain, which targets the activator to the correct promoter, and of activation domains, whose role is to enhance transcription (see references 21-23, 32, and 33 for reviews).The human snRNA gene family contains both RNA polymerase II and RNA polymerase III genes. The RNA polymerase II snRNA promoters consist of a proximal sequence element (PSE), which is sufficient to direct basal levels of transcription in vitro, and a distal sequence element, which activates basal transcription. The RNA polymerase III snRNA promoters are similar, except that basal transcription is directed by the combination of a PSE and a TATA box (reviewed in reference 9). The PSE is recognized by a multisubunit complex called the SNAP complex (SNAP c ) (7) or PTF (34). Since SNAP c can bind to the PSE on its own, it corresponds to a sequence-specific DNA binding basal transcription factor. SNAP c contains at least four subunits, SNAP43, SNAP45, SNAP50, and SNAP190, and cDNAs encoding the SNAP43 (7) or PTF ␥ (35), SNAP45 (24) or PTF ␦ (35), and SNAP50 (6) or PTF ␤ (2) su...

Diverse transcription factor binding features revealed by genome-wide ChIP-seq in C. elegans

“…GEI-11 is the ortholog of the DNA-binding SNAP190 component of the SNAPc complex, a well-characterized transcriptional regulator of snRNA genes (Wong et al 1998). Indeed, as expected based on this homology, GEI-11 binds to a higher fraction of snRNA genes than any other kind of ncRNA and is by far the most strongly associated with ncRNAs relative to coding genes, compared to all other factors (Fig.…”

Oct transcription factors mediate t(14;18) lymphoma cell survival by directly regulating bcl-2 expression

“…Certain isoforms of C/EBPb interact with both Oct-1 and Oct-2 on Ig heavy and light chain promoters, as well as in the absence of DNA, although this interaction was thought to interfere with transcriptional activation (Hatada et al, 2000). Oct-1 interacts with the Myb DNA-binding domain of the basal transcription factor SNAPc, and Oct-1 acts to recruit the TATA-binding protein TBP to a TATA box (Wong et al, 1998;Bertolino and Singh, 2002). In addition, Oct-1 can directly activate expression of Cdx2 (Jin and Li, 2001), another gene that is ectopically expressed in t(14;18) cells (Heckman et al, 2000).…”

Co-expression of multiple subunits enables recombinant SNAPC assembly and function for transcription by human RNA polymerases II and III

“…Antibody immunodepletion of HeLa cell nuclear extract was performed with either rabbit α-SNAP43 antiserum or preimmune sera as described previously [17,23]. In vitro transcription assays of human U1 and U6 snRNA genes were performed for 1 h at 30 °C using the depleted extracts as described previously [6,[27][28][29].…”

“…Presumably, components of SNAP C are differentially important for RNA polymerase II versus III transcription, although no evidence for subunit specialization has yet been uncovered. SNAP C is composed of at least five subunits, SNAP19 [17], SNAP43 [18,19], SNAP45 [19,20], SNAP50 [21,22], and SNAP190 [23]. SNAP190, the largest of the subunits, provides the fundamental scaffold for assembly of the complex and directly interacts with all other SNAP C subunits [24] and with TBP [25,26].…”