File:Ijms-18-00020-g001.B.png

English: Virion structure of influenza B virus (IBV): IBV is surrounded by a lipid bilayer containing the two viral glycoproteins hemagglutinin (HA), responsible for binding to sialic acid-containing receptors in the surface of susceptible cells, and neuraminidase (NA), responsible for viral release from infected cells. Furthermore, in the virion membrane is the ion channel BM2 and NB (IBV) proteins. Under the viral lipid bilayer is a protein layer composed of the M1 protein, which plays a role in virion assembly and budding, and the nuclear export protein (NEP) involved in the nuclear export of the viral ribonucleoprotein (vRNP) complexes. The eight viral segments and protein products are indicated inside the virions. Black lines at the end of each of the eight IBV vRNAs indicate the 3′ and 5′ non-coding regions (NCR). PB1 and PB2, polymerase basic 1 and 2; PA, polymerase acid; NP, nucleoprotein; NS, nonstructural gene; M: matrix; BM2: influenza B matrix protein 2.