FIG 4 .

Mapping of minor alleles that arose during culture onto the PDB 4WEF HPIV-3 HN crystal structure. The diagram shows the interface between the globular heads of two monomers, including receptor binding site II known to be critical for activation of F (discussed in text). At the top are sites located between residues 552 and 556 where we found minor allele variations in culture. At the bottom of the diagram, residues 239 and 242 are shown, where minor allele variations also arose from culture. Side chains are shown as they are in the reference strain—not the mutations that we noted.