A NOVEL RNA POLYMERASE-III TRANSCRIPTION FACTOR FRACTION THAT IS NOT REQUIRED FOR TEMPLATE COMMITMENT

We have identified and partially characterized a novel class III trans cription factor fraction (TFIIIE) from yeast nuclear extracts. TFIIIE is functionally distinct from the standard yeast transcription factor fractions, TFIIIB and TFIIIC. It is also different from either of the TFIIIB subfractions, B' and B''. TFIIIE is essential for specific tran scription of both tRNA and 5 S RNA genes, its activity is sensitive to proteinase K, and it exhibits an apparent sedimentation coefficient o f 4.0 S when analyzed on glycerol gradients. In the case of a tRNA gen e, TFIIIE does not play a role in the formation of stable preinitiatio n complexes containing TFIIIB and TFIIIC. It is required for single as well as multiple rounds of transcription, however. Thus, TFIIIE is in volved in the utilization of stable transcription complexes, but its a ction is not restricted to reinitiation events.