FIG. 1.

Protein prM cleavage-site mutants of TBEV. The envelope proteins prM (red) and E (green) are shown schematically at the top. Partial amino acid sequences are shown below for wild-type (WT) virus, the cleavage-deficient mutant prM(ΔR88), the revertant virus selected in BHK-21 cells [prM(ΔR88)-mf], mutant prM(ΔR88) serially passaged in the presence of trypsin [prM(ΔR88)+T], viral mutants isolated from prM(ΔR88)-infected mice [prM(ΔR88)-A, -B, and -C], and recombinant Cys mutants [prM(ΔR88/Y76C) and prM(ΔR88/C79Y)]. Numbers at the top refer to amino acid positions counted from the amino terminus of the respective protein. The furin cleavage site and mutated amino acid residues are shown in color. Positions relative to the site of cleavage in the wild-type sequence (depicted by an arrow) are numbered −1 to −4. The six conserved Cys residues (C) and the glycosylation site (⋄) of the “pr” part of protein prM are indicated. Triangles indicate single-residue deletion mutations; the (K) in protein E of mutant prM(ΔR88)-mf depicts a mutation that occurred in one of three passaging experiments (see details in the text).