Specific Interaction of TAFII105 with OCA-B Is Involved in Activation of Octamer-dependent Transcription

TAFII105 is a TFIID-associated factor highly expressed in B lymphocytes. This subunit is found in a small portion of TFIID complexes and is homologous to human TAFII130 and Drosophila TAFII110. In the present study we show that TAFII105 is involved in transcription activation directed by the B cell-specific octamer element found in many B cell-specific genes. B cells overexpressing TAFII105 display higher octamer-dependent transcription, whereas expression of a C-terminal truncated form of TAFII105 inhibits octamer transcription in a dominant negative manner. In addition, antibodies directed against TAFII105 specifically inhibit octamer-dependent transcription. Reporter gene analysis revealed that TAFII105 elevates octamer transcription in the presence of OCA-B, a cofactor subunit of Oct1 and Oct2 proteins. In vitro binding assays and functional studies established that the effect of TAFII105 on octamer activity involves interaction of TAFII105 with octamer-binding complexes via the C-terminal activation domain of OCA-B. These findings link TAFII105 coactivator function to B cell-specific transcription.