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 (TAFIIs) and other tissue-specific transcription components in regulating differential gene expression during development was not clear. Here we show that thecannonballgene ofDrosophilaencodes a cell type-specific homolog of a more ubiquitously expressed component of the general transcription factor TFIID.cannonballis required in vivo for high level transcription of a set of stage- and tissue-specific target genes during male gametogenesis. Regulation of transcription bycannonballis absolutely 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 TAFIIs play an important role in developmental regulation of gene expression.