VTRNA1-3 and infection: Previous studies have revealed that the hr1 and hr2 domains contain the principal determinants of receptor interaction, while the vr3 domain contributes to the specificity of receptor recognition for initiating effective infection but not to receptor binding affinity (Holmen et al., 2001; Melder et al., 2003; Federspiel, 2019; Munguia and Federspiel, 2019).