AN ATPASE COMPONENT OF THE TRANSCRIPTION ELONGATION COMPLEX IS REQUIRED FOR FACTOR-DEPENDENT TRANSCRIPTION TERMINATION BY VACCINIA RNA-POLYMERASE

Vaccinia virus RNA polymerase terminates transcription in response to a specific signal UUUUUNU in the nascent transcript. Transduction of t his signal to the elongating polymerase requires a virus-encoded termi nation factor, VTF. The existence of a second termination factor was s uggested by the finding that transient exposure of purified elongation complexes to heparin rendered them refractory to VTF-induced terminat ion. Loss of termination competence correlated with the removal of sev eral polypeptide components of the elongation complex. We present the identification of factor X, an activity that restored VTF responsivene ss to heparin-stripped ternary complexes. We propose that factor X, wh ich has an associated DNA-dependent ATPase activity, mediates the requ irement for ATP hydrolysis during transcription termination.