REARRANGEMENTS OF INTRANUCLEAR STRUCTURES INVOLVED IN RNA PROCESSING IN RESPONSE TO ADENOVIRUS INFECTION

We have studied in HeLa cells at the electron microscope level the res ponse to adenovirus infection of the RNA processing machinery. Compone nts of the spliceosomes were localized by in situ hybridization with b iotinylated U1 and U2 DNA probes and by immunolabeling with Y12 anti-S m monoclonal antibody, whereas poly(A)(+) RNAs were localized by speci fic binding of biotinylated poly(dT) probe. At early stages of nuclear transformation, the distribution of small nuclear RNPs was similar to that previously described in non-infected nuclei (Visa, N., Puvion-Du tilleul, F., Bachellerie, J. P. and Puvion, E., Eur. J. Cell Biol. 60, 308-321, 1993; Visa, N., Puvion-Dutilleul, F., Harper, F., Bachelleri e, J. P. and Puvion, E., Exp. Cell Res. 208, 19-34, 1993). As the infe ction progresses, the large virus-induced inclusion body consists of a central storage site of functionally inactive viral genomes surrounde d by a peripheral shell formed by clusters of interchromatin granules, compact rings and a fibrillogranular network in which are embedded th e viral single-stranded DNA accumulation sites. Spliceosome components and poly(A)(+) RNAs were then exclusively detected over the clusters of interchromatin granules and the fibrillogranular network whereas th e viral single-stranded DNA accumulation sites and compact rings remai ned unlabeled, thus appearing to not be directly involved in splicing. Our data, therefore, suggest that the fibrillogranular network, in ad dition to being the site of viral transcription, is also a major site of viral RNA splicing. Like the clusters of interchromatin granules, w hich had been already involved in spliceosome assembly, they could als o have a role in the sorting of viral spliced polyadenylated mRNAs bef ore export to the cytoplasm. The compact rings, which contain non-poly adenylated viral RNA, might accumulate the non-used portions of the vi ral transcripts resulting from differential poly(A)(+) site selection.