FIG. 3.

Median-joining network for the SU amino acid sequences of the viruses in all samples from three group 1 cats (Fig. 1). Solid and empty boxes are as described in the legend to Fig. 1. Stars and circles, substitutions conferring BNR at positions 481 and 557, respectively. Bootstrap values above 75% are indicated along the branches. The reticular pattern at the center depicts character conflicts. a and b, the two viral sequences obtained from cat 583 at 15 months p.i. in which position 481 was unsubstituted and substituted with a BNR-conferring amino acid, respectively. The considerable differences in branch lengths between these two sequences confirm the strong impact exerted by such a substitution on virus evolution.