VIRAL RIBONUCLEOPROTEIN COMPLEX-FORMATION AND NUCLEOLAR-CYTOPLASMIC RELOCALIZATION OF NUCLEOLIN IN POLIOVIRUS-INFECTED CELLS

The poliovirus 3' noncoding region (3'NCR) is involved in the efficien t synthesis of viral negative-stranded RNA molecules. A strong interac tion between a 105-kDa host protein and the wild-type 3'NCR, but not w ith a replication-defective mutant 3'NCR was detected. This 105-kDa pr otein was identified as nucleolin which predominantly resides in the n ucleolus and has been proposed to function in the folding of rRNA prec ursor molecules. A functional role for nucleolin in viral genome ampli fication was examined in a cell-free extract which has been shown to s upport the assembly of infectious virus from virion RNA. At early time s of viral gene expression, extracts depleted of nucleolin produced le ss infectious virus than extracts depleted of fibrillarin, another res ident of the nucleolus, indicating a functional role of nucleolin in t he early stages of the viral life cycle in this in vitro system. Immun ofluorescence analysis of uninfected and infected cells showed a nucle ocytoplasmic relocalization of nucleolin, but not of fibrillarin, in p oliovirus-infected cells. Relocalization of nucleolin was not simply a consequence of virally induced inhibition of translation or transcrip tion, because inhibitors of translation or transcription did not induc e nucleolar-cytoplasmic relocalization of nucleolin. These findings su ggest a novel virus-induced mechanism by which certain nucleolar prote ins are selectively redistributed in infected cells.