A POXVIRUS PROTEIN WITH A RING FINGER MOTIF BINDS ZINC AND LOCALIZES IN VIRUS FACTORIES

Shope fibroma virus (SFV) is a Leporipoxvirus closely related to the h ighly virulent myxoma virus. The DNA sequence of the BarnHI N fragment of the SFV DNA genome was determined, and the single complete open re ading frame (N1R) was characterized. The protein encoded by the N1R ge ne was found to contain a C,HC, RING finger motif at the C terminus. T his C3HC4 motif is the hallmark of a growing family of proteins, many of which are involved in regulation of gene expression, DNA repair, or DNA recombination. Complete homologs of the SFV N1R gene were also de tected in variola virus, myxoma virus, and vaccinia virus strain IHD-W . In contrast, the gene is completely absent from vaccinia virus strai n Copenhagen, and in vaccinia virus strain WR, the open reading frame is truncated prior to the zinc binding domain because of an ll-bp dele tion, thus producing a frameshift and premature stop codon. Recombinan t N1R protein from SFV was expressed in Escherichia coli and shown to bind zinc in a specific manner. Using fluorescence microscopy to visua lize a peptide epitope tag (derived from ICP27 of herpes simplex virus ) fused to the N terminus of the poxvirus proteins, we observed that t he N1R protein of SFV and its homologs in myxoma virus and vaccinia vi rus IHD W were localized primarily to the virus factories in the cytop lasm of infected cells and, to a lesser degree, the host cell nucleus. The truncated protein of vaccinia virus strain WR failed to localize in this manner but instead was observed throughout the cytoplasm.