TAF(II)250-independent transcription can be conferred on a TAF(II)250-dependent basal promoter by upstream activators.

TAF(II)250, a component of the general transcription factor, TFIID, is required for the transcription of a subset of genes, including those involved in regulating cell cycle progression. The tsBN462 cell line, with a temperature-sensitive mutation of TAF(II)250, grows normally at 32 degrees C, but when grown at 39.5 degrees C, it differentially arrests transcription of many, but not all, genes. The present studies examine the basis for the requirement for TAF(II)250. We show that the basal promoter of a major histocompatibility complex class I gene requires TAF(II)250. This dependence can be overcome by select upstream regulatory elements but not by basal promoter elements. Thus, the coactivator CIITA rescues the basal promoter from the requirement for TAF(II)250, whereas introduction of a canonical TATAA box does not. Similarly, the SV40 basal promoter is shown to require TAF(II)250, and the presence of the 72-base pair enhancer overcomes this requirement. Furthermore, the SV40 72-base pair enhancer when placed upstream of the basal class I promoter renders it independent of TAF(II)250. These data suggest that the assembly of transcription initiation complexes is dynamic and can be modulated by specific transcription factors.