Figure 2
MLD 50 of CZ and JY viruses and their recombinant viruses. Red and blue boxes indicate the derivation of virus gene segments or PB2 amino acids. MLD50 was determined for each indicated virus in 6-week-old female BALB/c mice. A MLD50 of wild type (wt) or rescued (r) CZ (or JY) virus and its reassortant viruses containing single, double or triple genes from the JY (or CZ) virus. B MLD50 of r-CZ (or r-JY) and its recombinant viruses with indicated single or double substitutions in the PB2. NA, not available, recused not successful.