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 requ ired for the transcription of a subset of genes, including those involved i n regulating cell cycle progression. The tsBN462 cell line, with a temperat ure-sensitive mutation of TAF(II)250, grows normally at 32 degrees C, but w hen grown at 39.5 degrees C, it differentially arrests transcription of man y, but not all, genes. The present studies examine the basis for the requir ement for TAF(II)250. We show that the basal promoter of a major histocompa tibility complex class I gene requires TAF(II)250. This dependence can be o vercome by select upstream regulatory elements but not by basal promoter el ements. Thus, the coactivator CIITA rescues the basal promoter from the req uirement 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, an d the presence of the 72-base pair enhancer overcomes this requirement. Fur thermore, 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 t hat the assembly of transcription initiation complexes is dynamic and can b e modulated by specific transcription factors.