Kaposi's Sarcoma-Associated Herpesvirus ORF57 Is Not a Bona Fide Export Factor

Kaposi's sarcoma-associated herpesvirus (KSHV [human herpesvirus 8; HHV-8]) open reading frame 57 (ORF57) is a viral early protein participating in posttranscriptional regulatory events, such as splicing, RNA stabilization, and protein expression. Recent data suggest that ORF57 recruits the transcription and export (TREX) complex to viral RNA and exports these transcripts to the cytoplasm. In this study, we show that although ORF57 promotes expression of a selection of KSHV viral intronless RNAs, it is not a bona fide export factor.