A map of protein-protein contacts within the small nuclear RNA-activating protein complex SNAP(c)

The nucleation of RNA polymerases I-III transcription complexes is usually directed by distinct multisubunit factors. In the case of the human RNA pol ymerase II and III small nuclear RNA (snRNA) genes, whose core promoters co nsist of a proximal sequence element (PSE) and a PSE combined with a TATA b ox, respectively, the same multisubunit complex is involved in the establis hment of RNA polymerase II and III initiation complexes. This factor, the s nRNA-activating protein complex or SNAP(c), binds to the PSE of both types of promoters and contains five types of subunits, SNAP190, SNAP50, SNAP45, SNAP43, and SNAP19, SNAP(c) binds cooperatively with both Oct-1, an activat or of snRNA promoters, and in the RNA polymerase III snRNA promoters, with TATA-binding protein, which binds to the TATA box located downstream of the PSE. Here we have defined subunit domains required for SNAP, subunit-subun it association, and we show that complexes containing little more than the domains mapped here as required for subunit-subunit contacts bind specifica lly to the PSE, These data provide a detailed map of the subunit-subunit in teractions within a multifunctional basal transcription complex.