The ORF49 protein of murine gammaherpesvirus 68 cooperates with RTA in regulating virus replication

Our functional mapping study of murine gammaherpesvirus 68 (MHV-68, or γHV-68) revealed that a mutant harboring a transposon at the ORF49 locus (ORF49^null) evidenced a highly attenuated in vitro growth. ORF49 resides adjacent to and in an opposite direction from RTA, the primary switch of the gammaherpesvirus life cycle. A FLAG-tagged ORF49 protein was able to transcomplement ORF49^null, and a revertant of ORF49^null restored its attenuated growth to a level comparable to that of the wild type. The FLAG-tagged ORF49 protein promoted the ability of RTA to activate downstream target promoters and enhanced virus replication from the ORF50^null virus in the presence of RTA. Furthermore, ORF49 enhanced wild-type virus replication by increasing the RTA transcript levels. Our data indicate that ORF49 may perform an important function in MHV-68 replication in cooperation with RTA.