HUMAN TRANSCRIPTION FACTOR-IIIC BOX-B BINDING SUBUNIT

Transcription factor IIIC (TFIIIC) is a multisubunit basic TF for RNA polymerase III. It initiates transcription complex assembly on tRNA an d related genes by binding to the internal box B promoter element and is also required for transcription of 5S rRNA and other stable nuclear and cytoplasmic RNAs transcribed by polymerase III. In mammalian cell s, regulation of TFIIIC activity controls overall polymerase III trans cription in response to growth factors and viral infection. Here, we r eport the cloning and sequencing of a full-length cDNA (and genomic DN A from the transcription initiation region) encoding the box B binding subunit of human TFIIIC, the 243-kDa alpha subunit. Specific antisera raised against the encoded protein super shifts a TFIIIC-box B DNA co mplex during an electrophoretic mobility shift assay and immunodeplete s TFIIIC transcriptional activity from a partially purified TFIIIC fra ction, proving that the cDNA encodes a component of TFIIIC. The human protein shows surprisingly little similarity to the box B binding subu nit of yeast TFIIIC.