Mutations were introduced in the transmembrane region of the spike protein of the murine coronavirus A59. The maturation of these mutant S proteins was not affected, they were all expressed at the cell surface, and became acylated, however some mutant S proteins did not induce cell-to-cell fusion. An I-->K change in the middle of the predicted transmembrane (TM) anchor and mutation of the first three cysteine residues of the TM domain resulted in a fusion-negative phenotype. We propose a model by which these data can be explained.
Site directed mutagenesis of the murine coronavirus spike protein. Effects on fusion.