Blok and Air 1982b; Fields et al. 1981 is one of the two major glycoproteins on the virus surface.
Varghese and Colman, 1991 it is encoded by segment 6 of influenza A virus. The three dimensional structure of the NA revealed that the NA monomer consists of four domains: a box – shaped globular head, a thin stalk, a transmembrane domain, and a cytoplasmic domain.
Colman et al. 1983; Varghese et al. 1983 the box-shaped head contains the major antigenic sites & enzyme active center.
Deena, et al showed that the short stalk length of an avian virus NA reduce viral transmission & reduce its ability to penetrate mucous & deaggregate virions.