Regulation of a TATA-binding protein-associated factor during cellular differentiation.

RNA polymerase III transcription is down-regulated when F9 embryonal carcinoma cells differentiate into parietal endoderm. This reflects a decrease in the activity of TFIIIB, a multisubunit complex that is required for all class III gene expression. Two essential components of TFIIIB are the TATA-binding protein (TBP) and an associated polypeptide called BRF that is specific to this complex. The abundance of both TBP and BRF decreases during F9 cell differentiation. Whereas the amount of TBP assembled into TFIIIB is down-regulated, this is not the case for all TBP-containing complexes. BRF levels show a more dramatic decline that appears sufficient to account for the overall change in transcriptional activity. Developmental regulation of a specific class of genes may therefore be achieved through changes in the availability of a TBP-associated factor.