ISOLATION OF TRANSCRIPTION FACTOR-IIIC FROM DICTYOSTELIUM-DISCOIDEUM

Transcription factor IIIC (TFIIIC) binds in a sequence specific manner to RNA-polymerase-III-transcribed genes (e.g. tRNA genes). It sequest ers other transcription factors into the preformed complex, thereby ac tivating transcription by RNA polymerase III. The Dictyostelium discoi deum homologue of TFIIIC was highly purified by affinity chromatograph y based on its tDNA-binding activity. This TFIIIC homologue is a multi component factor (molecular mass 380 kDa), which binds to the B-box el ement of the internal tRNA gene promoter without significant A-box int eraction. Partially purified D. discoideum TFIIIC is able to functiona lly complement a human RNA polymerase III in vitro transcription syste m depleted of human TFIIIC. We provide evidence that partially purifie d D. discoideum TFIIIC interacts in vitro with gene-external B-box ele ments present downstream of many D. discoideum tRNA genes.