Developmental regulation of transcription by a tissue-specific TAF homolog

Alternate forms of the general transcription machinery have been described in several tissues or cell types. However, the role of tissue-specific TBP- associated factors (TAF(II)s) and other tissue-specific transcription compo nents in regulating differential gene expression during development was not clear. Here we show that the cannonball gene of Drosophila encodes a cell type-specific homolog of a more ubiquitously expressed component of the gen eral transcription factor TFIID. cannonball is required in vivo for high le vel transcription of a set of stage- and tissue-specific target genes durin g male gametogenesis. Regulation of transcription by cannonball is absolute ly required for spermatogenesis, as null mutations block meiotic cell cycle progression and result in a complete failure of spermatid differentiation. Our results demonstrate that cell type-specific TAF(II)s play an important role in developmental regulation of gene expression.