FIG 4.

Internal deletions occurred in the NS segment of WT-Venus-PR8. (A) Schematic sequence of the NS segment in WT-Venus-PR8 viruses that lost Venus expression after serial passages in MDCK cells. Selected examples are shown. (B) The procedure for the coinfection experiment is illustrated. The synonymous mutation was introduced into the 3′ or 5′ region of the NS segment of WT-Venus-PR8. The viruses were then used to coinfect MDCK cells. Viruses not expressing Venus were plaque purified, and the sequences of their NS segments were analyzed. (C) Examples of the sequences of the NS segment of Venus-negative viruses obtained after coinfection experiments. The red “X” indicates an introduced synonymous mutation.