NUCLEAR-ORGANIZATION OF SPLICING SMALL NUCLEAR RIBONUCLEOPROTEINS IN ADENOVIRUS-INFECTED CELLS

We have studied the effect of adenovirus infection on the nuclear orga nization of splicing small nuclear ribonucleoproteins (snRNPs) in HeLa cells. In uninfected HeLa cells, snRNPs are widespread throughout the nucleoplasm but also are concentrated in specific nuclear structures, including coiled bodies, interchromatin granules, and perichromatin f ibrils. We have used immunofluorescence microscopy to study the locali zation of splicing snRNPs relative to centers of viral DNA synthesis a nd accumulation identified with antiserum against the viral 72,000-mol ecular-weight single-stranded DNA-binding protein (72K protein). Splic ing snRNPs were independently detected with both monoclonal and polycl onal antibodies specific for common snRNP antigens, snRNP-specific pro teins, and the snRNA-specific 2,2,7-trimethylguanosine 5' cap structur e. We have examined infected cells 2 to 24 h after infection, and, in the majority of these cells, we observed no colocalization of the snRN P and 72K-protein staining patterns. In the late phase, snRNPs were fo und to markedly concentrate in discrete clusters that were distinct fr om the centers of viral DNA synthesis and accumulation identified with anti-72K protein. We have treated cells with hydroxyurea at various t imes after infection to inhibit aspects of the virus infectious progra m. We have found that the accumulation of snRNP clusters is correlated with late gene expression rather than with DNA synthesis or early gen e expression. Finally, we show that the late-phase snRNP clusters colo calize with a monoclonal antibody that primarily stains interchromatin granules. These results suggest that the centers of snRNP concentrati on in late-phase infected cells are likely to correspond to interchrom atin granule clusters.