REGULATION OF A TATA-BINDING PROTEIN-ASSOCIATED FACTOR DURING CELLULAR-DIFFERENTIATION

RNA polymerase III transcription is down-regulated when F9 embryonal c arcinoma cells differentiate into parietal endoderm. This reflects a d ecrease in the activity of TFIIIB, a multisubunit complex that is requ ired for all class III gene expression. Two essential components of TF IIIB 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 f or all TBP-containing complexes. BRF levels show a more dramatic decli ne that appears sufficient to account for the overall change in transc riptional activity. Developmental regulation of a specific class of ge nes may therefore be achieved through changes in the availability of a TBP-associated factor.