Sequence of interrupted and uninterrupted mRNAs and cloned DNA coding for the two overlapping nonstructural proteins of influenza virus

We have obtained the complete sequence of cloned full-length DNA (NS DNA) derived from influenza virus gene 8, which codes for two unique polypeptides, NS₁ and NS₂, and the sequence of the NS₂ mRNA. Previously we showed that the mRNA for NS₁ (∼860 nucleotides) is colinear with the viral RNA and maps from 0.05−0.95 units of the cloned NS DNA, and the body of the NS₂ mRNA (∼340 nucleotides) maps from 0.59−0.95 units, suggesting that the two mRNAs are 3′ co-terminal and share the same poly(A) addition site. Sequencing studies have shown that the NS₂ mRNA contains an interrupted sequence of 473 nucleotides. The nucleotide sequences at the junctions of the interrupted segment are similar to those of the consensus sequences at the splicing sites of intervening regions in eucaryotic mRNAs. The first ∼56 virus-specific nucleotides at the 5′ end of the NS₂ mRNA are the same nucleotides as are found at the 5′ end of the NS₁ mRNA, and this leader sequence of the NS₂ mRNA contains the initiation codon for protein synthesis and coding information for nine amino acids which would be common to NS₁ and NS₂. In addition, both mRNAs contain 10–20 heterogeneous nonviral nucleotides at their 5′ ends. The ∼340 nucleotide body region of the NS₂ mRNA can be translated in the +1 reading frame, and the sequence indicates that NS₁ and NS₂ overlap by 70 amino acids that are translated from different reading frames.