Effects of a Temperature Sensitivity Mutation in the J1R Protein Component of a Complex Required for Vaccinia Virus Assembly

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Abstract
Vaccinia virus J1R protein is required for virion morphogenesis (W. L. Chiu and W. Chang, J. Virol. 76: 9575-9587, 2002). In this work, we further characterized the J1R protein of wild-type vaccinia virus and compared it with the protein encoded by the temperature-sensitive mutant virus C ts 45. The mutant C ts 45 was found to contain a Pro-to-Ser substitution at residue 132 of the J1R open reading frame, which is responsible for a loss-of-function phenotype. The half-life of the J1R-P132S mutant protein was comparable at both 31 and 39°C, indicating that the P132S mutation did not affect the stability of the J1R protein. We also showed that the J1R protein interacts with itself in the virus-infected cells. The N-terminal region of the J1R protein, amino acids (aa) 1 to 77, interacted with the C-terminal region, aa 84 to 153, and the P132 mutation did not abolish this interaction, as determined by two-hybrid analysis. Furthermore, we demonstrated that J1R protein is part of a viral complex containing the A30L, G7L, and F10L proteins in virus-infected cells. In immunofluorescence analyses, wild-type J1R protein colocalized with the A30L, G7L, and F10L proteins in virus-infected cells but the loss-of-function P132 mutant did not. Furthermore, without a functional J1R protein, rapid degradation of A30L and the 15-kDa forms of the G7L and F10L proteins was observed in cells infected with C ts 45 at 39°C. This study thus demonstrated the importance of the J1R protein in the formation of a viral assembly complex required for morphogenesis.