DYNAMIC ORGANIZATION OF SPLICING FACTORS IN ADENOVIRUS-INFECTED CELLS

Adenovirus infection affects the nuclear distribution of host splicing factors. Late phase-infected cells contain discrete clusters of small nuclear ribonucleoproteins (snRNPs) that are separate from centers co ntaining the viral 72-kilodalton DNA-binding protein (72K protein). In the present study, we demonstrate that these snRNP clusters also cont ain splicing factors from the SR protein family. We show that a previo usly described monoclonal antibody, 3C5, detects SR proteins. Furtherm ore, we demonstrate that late region 3 transcription occurs at a maxim al rate in infected cultures in which greater than 90% of the cells co ntain the snRNP clusters, indicating that such cells are actively tran scribing their late genes. During the onset of the late phase, the int ranuclear distribution of splicing factors is very different from that seen after the late phase is established. When late viral transcripti on commences, cells with snRNP clusters are less prevalent than in cul tures that are maintaining maximum levels of late transcription. Inste ad, a cell type which shows snRNPs, concentrated in foci that also con tain the viral 72K DNA-binding protein is detected. This cell type dis appears from cultures by 18 to 20 h after a high-multiplicity infectio n. These results suggest a dynamic organization of splicing factors in infected cells that can be correlated to the status of viral gene exp ression. Our work also provides an explanation for the differing resul ts that have been published concerning the organization of splicing fa ctors in the adenovirus-infected cell nucleus (L. F. Jimenez-Garcia an d D. L. Spector, Cell 73:47-59, 1993). During the present study we obs erved that a monoclonal antibody against the SC-35 protein, which was used by Jimenez-Garcia and Spector to study the localization of the SC -35 splicing factor in adenovirus-infected cells, cross-reacts with th e adenovirus 72K DNA-binding protein and is thus unsuitable for this t ype of study.