Table III. Membrane fusion efficiencies of L447 and I449 mutant F proteins.
| Syncytiaa | Syncytiaa | R18 dyed | CF dyee | R18 dyed | CF dyee | |
|---|---|---|---|---|---|---|
| +HNb | −HNc | +HN f | +HN f | −HN g | −HN g | |
| SV5 F wtf | ++ | ++ | 105 ± 10 | 107 ± 13 | 34 ± 4 | 34 ± 5 |
| L447G | ++ | − | 65 ± 5 | 66 ± 6 | 1 ± 1 | 1 ± 1 |
| L447A | ++ | − | 82 ± 7 | 80 ± 6 | 0 ± 1 | 0 ± 1 |
| L447V | ++ | − | 83 ± 13 | 83 ± 10 | 3 ± 1 | 3 ± 1 |
| L447I | ++ | + | 97 ± 9 | 94 ± 9 | 16 ± 3 | 17 ± 3 |
| L447F | +++ | +++ | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
| L447W | +++ | +++ | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
| I449G | − | − | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
| I449A | + | − | 85 ± 6 | 84 ± 7 | 1 ± 1 | 1 ± 1 |
| I449V | + | − | 89 ± 8 | 88 ± 7 | 2 ± 1 | 2 ± 1 |
| I449L | ++ | + | 67 ± 6 | 65 ± 4 | 2 ± 1 | 1 ± 1 |
| I449F | +++ | +++ | 12 ± 3 | 11 ± 3 | 5 ± 2 | 5 ± 2 |
| I449W | +++ | +++ | 18 ± 2 | 18 ± 3 | 3 ± 1 | 3 ± 2 |
| S443P | +++ | +++ | 168 ± 7 | 166 ± 6 | 139 ± 8 | 138 ± 8 |
a
Syncytia assays performed 20 h after transfection on monolayers of BHK 21F cells. The extents of syncytia formation were ranked as follows: +++, noticeably greater than wt; ++, similar to wt; +, noticeably less than wt; −, no syncytia formation.
b
F protein coexpressed with SV5 HN.
c
Assay performed in the absence of HN transfection.
d
Average number of R18 lipid dye transfer events per microscopic field from target RBCs to effector CV-1 cells expressing F mutants.
e
Average number of CF aqueous dye transfer events per microscopic field from target RBCs to effector CV-1 cells expressing F mutants.
f
F protein coexpressed with SV5 HN.
g
F protein coexpressed with uncleaved influenza virus HA as an RBC-binding protein.