The influenza C virus genome consists of seven single-stranded RNA segments of negative polarity. The hemagglutinin-esterase (HE) glycoprotein of influenza C virus has three biological activities, i.e. receptor-binding activity for N-acetyl-9-O-acetylneuraminic acid, fusion activity, and receptor-destroying activity, which is a neuraminate-O-acetylesterase. Unspliced mRNA from RNA segment 6 is first translated into a 374-amino-acid protein, P42. P42 is cleaved by signal peptidase, producing M1' and CM2 proteins, composed of the N-terminal 259 amino acids and the C-terminal 115 amino acids, respectively. Xenopus laevis oocytes expressing influenza C virus CM2 protein demonstrated that CM2 protein forms a voltage-activated ion channel permeable to chloride ion.