Identification of a response element in a herpesvirus saimiri mRNA recognized by the ORF57 protein

The herpesvirus saimiri (HVS) ORF57 protein binds viral RNA, enabling the efficient nuclear export of intronless viral mRNAs. However, it is not known how ORF57 recognizes these viral mRNAs. In this study, a systematic evolution of ligands by exponential enrichment (SELEX) approach was used to select RNA sequences that are preferentially bound by the ORF57 protein. Results identified a recurring motif, GAAGRG, within the majority of selected RNAs, which is also present in many late HVS mRNAs. RNA immunopreciptations demonstrated that disruption of this motif within a viral intronless RNA ablates ORF57 binding. These data suggest that the GAAGRG motif may be required within a HVS intronless mRNA for recognition by the ORF57 protein.