Nucleotide sequence of RNA segment 7 of influenza B/Singapore/222/79: maintenance of a second large open reading frame.

The nucleotide sequence of RNA segment 7 of influenza B/Singapore/222/79 has been determined. The deduced amino acid sequence of the M1 protein indicates that it contains 248 amino acids of which 243 are identical in the B/Lee/40 M1 protein. A second overlapping open reading frame with a maximum coding region of 195 amino acids has also been maintained in the 39 years separating the two isolates. The deduced amino acid sequence of the second coding region displays 86% homology with the comparable B/Lee/40 sequence (27 changes). The conservation of the second open reading frame suggests that this region is important in the replicative cycle of influenza B viruses.