A HERPES-SIMPLEX VIRUS TYPE-1 IMMEDIATE-EARLY GENE-PRODUCT, IE63, REGULATES SMALL NUCLEAR RIBONUCLEOPROTEIN DISTRIBUTION

Herpes simplex virus 1 (HSV-1), a nuclear replicating DNA virus, has 7 3 identified genes of which only 4 contain introns. For this reason th e virus probably makes only minimal use of the cellular RNA-splicing m achinery. Antigens associated with the small nuclear ribonucleoprotein particles (snRNPs) that are subunits of splicing complexes have been reported to redistribute in the nucleus and become concentrated into t he intranuclear structures, the interchromatin granules, after HSV-1 i nfection [Martin, T. E., Barghusen, S. C., Leser, G. P. & Spear, P. G. (1987) J. Cell Biol. 105, 2069-2082]. We observe this snRNP redistrib ution upon HSV-1 infection, in which the widespread snRNP staining pat tern changes to a restricted punctate distribution with a concomitant loss of coiled bodies in HSV-1-infected cells. We show here that expre ssion of the immediate-early (IE) subset of HSV-1 genes is necessary a nd sufficient for snRNP redistribution. Using a series of HSV-1 mutant s in different IE genes, we have established that specifically the pro duct of the viral IE63 (ICP27) gene is essential for this effect, and transfection experiments revealed that IE63 expression alone can cause the snRNP redistribution. Further, we show that the IE63 gene product colocalizes with the redistributed snRNP in the nucleus. The snRNP re distribution caused by HSV-1 infection resembles the effect seen after inhibition of transcription in uninfected cells. In HSV-1-infected ce lls, however, the snRNP redistribution is under the control of viral I E gene products and occurs during active virus gene transcription.