Abstract: To explore the effects of mutations at the E2 protein leucine sites on specific membrane fusion in rubella virus (RV). MethodsNine leucine sites were chosen from E2 protein, and sitedirected mutagenesis was used to obtain corresponding mutants. All mutants and wild type proteins were expressed in BHK21 cells and treated with acid media to induce specific cell fusions. Expression efficiencies of mutant proteins on cell surfaces were quantified with fluorescenceactivated cell sorter (FACS). The fusion functions were separately assayed with Giemsa staining and a reporter gene method for qualitative and quantitative analysis. Hemadsorption assays were performed to qualitatively and quantitatively detect binding activity of mutant proteins. ResultsThe FACS indicated that expression efficiencies of all mutant proteins except for L144A and L225A were lower than those of the wild type proteins. When effects of lower cell surface expression efficiencies were eliminated, the cell fusion activities of all mutant proteins were lower than those of wild type proteins, especially those of mutants L58A, L105A, L128A and L144A. Hemadsorption assays demonstrated that binding abilities of mutants L58A, L105A, L128A and L144A were decreased, but those of the other five mutant proteins were almost the same as wild type proteins. ConclusionThe L58L144 region in E2 protein is important for specific membrane fusion.

Key words: Rubella virus, Membrane fusion, Envelope glycoprotein