Herpes simplex virus type 1 immediate early protein IE63 shuttles between nuclear compartments and the cytoplasm

Herpes simplex virus type 1 (HSV-1) immediate early protein IE63, an essential nuclear protein, is pleiotropic in function and, at the post-transcriptional level, inhibits RNA splicing, interacts with cellular splicing small nuclear ribonucleoprotein particles (snRNPs), binds RNA and prevents the nucleocytoplasmic transport of intron-containing mRNAs. Here it is reported that IE63 is a nucleocytoplasmic shuttle protein able to travel from snRNP- and RNA-rich nuclear foci to the cytoplasm, where it accumulates during actinomycin D treatment. This newly identified property suggests that IE63 facilitates nuclear export of HSV-1 transcripts, in addition to retaining intron-containing transcripts in the nucleus. The mechanism by which IE63 controls RNA export has yet to be defined.