Anchorage of adenoviral RNAs to clusters of interchromatin granules.

Previous in situ hybridization experiments have revealed that clusters of interchromatin granules in adenovirus type 5 infected HeLa cells contain not only spliceosome components but also significant amounts of viral RNA and poly(A)+ RNA molecules whereas nonpolyadenylated viral RNA molecules are present within the still enigmatic viral compact rings. To determine the levels of association of the viral RNA molecules with cellular clusters of interchromatin granules and viral compact rings, we investigated the effects of a cell extraction technique on these structures. The spreading apart of the nucleoproteins by exposure of infected cells to a detergent-containing hypotonic solution, which exclusively preserves structurally linked components, resulted in the persistence within the clusters of interchromatin granules of U1 snRNA, U2 snRNA, viral RNA, and poly(A)+ RNA. These data clearly reveal that, in addition to the well-known strong binding of spliceosome components within the clusters of interchromatin granules, there also is an anchorage of viral RNA and messenger RNA molecules to these structures, which suggests functional relationships. Taken together, the data indicate that the clusters of interchromatin granules might be the sites of accumulation and retention of those cell and viral messenger RNA molecules that are transiently stored in the nucleus before their degradation or their transport to the cytoplasm. In addition, the firm binding of nonpolyadenylated viral RNA to the viral compact rings suggests a role for these structures in the transient storage of the nonused portions of the viral primary late transcripts.