DNA-dependent ATPase that acts as a 5' to 3' translocase on single-stranded DNA and thereby plays a role in transcription termination of viral early genes. Uses forward translocation in concert with the viral RNA polymerase RAP94/OPG109 subunit and the capping enzyme/VTF to catalyze release of UUUUUNU-containing nascent RNA from the elongation complex. In addition, acts as a positive elongation factor to assist transcription through problematic sequences