NTP-dependent helicase that catalyzes unidirectional unwinding of 3'tailed duplex RNAs and plays an important role during transcription of early mRNAs, presumably by preventing R-loop formation behind the elongating RNA polymerase. Might also play a role in the export of newly synthesized mRNA chains out of the core into the cytoplasm. Required for replication and propagation of viral particles. ATP + H2O = ADP + H(+) + phosphate Monomer. Localizes to the virion core. Expressed both early and late in the viral replicative cycle. Belongs to the DEAD box helicase family. DEAH subfamily.