A TBP–TAF complex required for transcription of human snRNA genes by RNA polymerases II and III

Abstract

THE TATA-box-binding protein TBP exists in the cell complexed with different sets of TBP-associated factors (TAFs)¹. In general, each of these TBP–TAF complexes is dedicated to transcription by a single RNA polymerase. 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 SNAPc¹¹. Unlike the other TBP–TAF complexes, SNAPc is implicated in transcription by two types of polymerases; it is required for transcription of both the RNA polymerase II and 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 amino-acid sequence of SNAP43 reveals that it corresponds to a new protein.