Plaque growth of influenza A/WSN/33 (H1N1) viruses carrying mutations in hemagglutinin.

Results are for wildtype (WT), temperature-sensitive (ts), and ts
virus with predicted stabilizing mutations. The plaques are scored
as ++ for clear plaques, + for smaller or
opaque plaques, +/− for barely distinguishable
plaques, − for no plaques, and ND for not determined. The
first mutation numbers are for sequential numbering of the A/WSN/33
hemagglutinin sequence beginning with zero at the N-terminal
methionine, while the numbers in parentheses correspond to those
used in the crystal structure with PDB code 1RVZ.