Putative initiation factor. Necessary for efficient transcription elongation past template-encoded arresting sites. Isoform 1 contains the N-terminal region that is probably responsible for the initiation function (PubMed:32075923). Expressed in the intermediate phase of the viral replicative cycle. Expressed in the early phase of the viral replicative cycle. Expressed in the late phase of the viral replicative cycle. Belongs to the TFS-II family.