INFLUENZA-VIRUS NS1 PROTEIN ALTERS THE SUBNUCLEAR LOCALIZATION OF CELLULAR SPLICING COMPONENTS

Intranuclear structure was studied in influenza virus-infected cells b y immunofluorescence microscopy with antibodies specific for fibrillar in, the splicing factor SC35 and the autoantigen p80 coilin. In the co urse of the infection, an increase in the number of coiled bodies was observed, with a parallel decrease in their size. In addition, the nor mal speckled pattern of the SC35 factor was altered to generate a more punctate distribution. However, no alteration was observed in the fib rillarin staining pattern. Since an alteration in the splicing of both viral and cellular mRNAs upon expression of influenza virus NS1 prote in has been reported previously, the possible effects of NS1 expressio n on intranuclear structure were assayed. The increase in the coiled b ody numbers was not specific for the expression of NS1 protein, but al terations in the nuclear location of small ribonucleoprotein particles , as determined by immunofluorescence with an anti-Sm serum or the SC3 5 splicing factor, were produced by the sole expression of NS1 protein . These results correlate with the previously reported inhibition of s plicing induced by NS1 protein expression and suggest an interaction o f this influenza virus protein with the cellular splicing machinery.