DNA helicase which seems to act as a postreplicative transcription termination factor. Involved in ATP-dependent release of nascent RNA. Forms a stable complex with single-stranded DNA, and to a lesser extent RNA (By similarity). Interacts with G2. Might be part of a transcription complex composed at least of G2, A18, and H5. Localizes to the virion core. Belongs to the helicase family. Poxviruses subfamily.