HUMAN TAF(PARALLEL-TO)105 IS A CELL-TYPE-SPECIFIC TFIID SUBUNIT RELATED TO HTAF(PARALLEL-TO)130

We previously characterized Drosophila and human TAF subunits that mak e up the core TFIID complex found in all cells. Here, we report that d ifferentiated B cells contain a novel substoichiometric TAF of 105 kDa not found associated with TFIID isolated from other cell types. The c DNA encoding hTAF(II)105 reveals a highly conserved C-terminal domain shared by hTAF(II)130 and dTAF(II)110, while the N-terminal coactivato r domain has diverged significantly. All cells tested express TAF(II)1 05 mRNA, but only B cells contain significant levels of protein associ ated with TFIID. Transient overexpression of hTAF(II)105 selectively s quelches the transcription of some genes in B cells. These properties suggest that TAF(II)105 is a cell type-specific subunit of TFIID that may be responsible for mediating transcription by a subset of activato rs in B cells.