In addition, the results of the competitive blocking test with point mutants revealed that all sites (G199, V200, P201, W202, Y203, L204 and G205) in residues 199–205 of hr1; R274 in residues 269–275 of hr2; and G324, I326 and 328_329insP in residues 323–331 of vr3 played important roles in competitively blocking RCASBP(A) infection according to the binding of the soluble recombinant ALV-A gp85 point mutants to DF-1 cell surface receptors. Here, VTRNA1-3 is linked to infection.