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_cconsists 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.

ACKNOWLEDGMENTS

We thank Winship Herr and Vivek Mittal for comments on the manuscript. We also thank Spencer Teplin for oligonucleotide synthesis and James Duffy, Michael Ockler, and Philip Renna for artwork and photography.

This work was supported in part by National Institutes of Health grant RO1GM38810 to N.H. and a grant from the Swiss National Fund to M.S.