A TBP-TAF COMPLEX REQUIRED FOR TRANSCRIPTION OF HUMAN SNRNA GENES BY RNA-POLYMERASE-II AND RNA-POLYMERASE-III

THE TATA-box-binding protein TBP exists in the cell complexed with dif ferent sets of TBP-associated factors (TAFs)(1). In general, each of t hese TBP-TAP complexes is dedicated to transcription by a single RNA p olymerase. Thus, SL1, TFIID and TFIIIB are required for transcription by polymerases I, II and III, respectively(2-10). Here we characterize a fourth TBP-TAF complex called SNAPc(11). Unlike the other TBP-TAF c omplexes, SNAPc is implicated in transcription by two types of polymer ases; it is required for transcription of both the RNA polymerase II a nd III small-nuclear RNA genes and binds specifically to the proximal sequence element PSE, a non-TATA-box basal promoter element common to these two types of genes(11-13). In addition to TBP, SNAPc is composed of at least three TAFs, SNAP43, SNAP45 and SNAP50. The predicted amin o-acid sequence of SNAP43 reveals that it corresponds to a new protein .