SPLICED EXONS OF ADENOVIRUS LATE RNAS COLOCALIZE WITH SNRNP IN A SPECIFIC NUCLEAR DOMAIN

Posttranscriptional steps in the production of mRNA include well chara cterized polyadenylation and splicing reactions, but it is also necess ary to understand how RNA is transported within the nucleus from the s ite of its transcription to the nuclear pore, where it is translocated to the cytoplasmic compartment. Determining the localization of RNA w ithin the nucleus is an important aspect of understanding RNA producti on and may provide clues for investigating the trafficking of RNA with in the nucleus and the mechanism for its export to the cytoplasm, We h ave previously shown that late phase adenovirus-infected cells contain large clusters of snRNP and non-snRNP splicing factors; the presence of these structures is correlated with high levels of viral late gene transcription. The snRNP clusters correspond to enlarged interchromati n granules present in late phase infected cells, Here we show that pol yadenylated RNA and spliced tripartite leader exons from the viral maj or late transcription unit are present in these same late phase snRNP- containing structures. We find that the majority of the steady state v iral RNA present in the nucleus is spliced at the tripartite leader ex ons. Tripartite leader exons are efficiently exported from the nucleus at a time when we detect their accumulation in interchromatin granule clusters. Since the enlarged interchromatin granules contain spliced and polyadenylated RNA, we suggest that viral RNA may accumulate in th is late phase structure during an intranuclear step in RNA transport.