The persistent variant of influenza C virus carries one characteristic point mutation in RNA segment 1

Influenza C/Ann Arbor/1/50-pi (C/AA-pi) virus causes persistent infections in MDCK and Wi38 cells, but sets limited, wild-type like infections in other cells. Concluding that persistence itself is dependent on the host environment, we determined the nucleotide sequence of the C/AA-pi analogous gene to the basic polymerase 2 (PB2) of influenza A virus, which is known to be a determinant for the host range. C/AA-pi and the parental wild-type virus (C/AA-wt) have 16 nucleotides in common that are different to a previously published PB2 sequence (C/JJ/50). These variations, which are probably due to divergent passage histories, are scattered along the sequence and are partially found in another published isolate (C/Berlin/1/85). One single mutation, however, is unique to the persistent variant. Nucleotide 28 mutated from T to C which leads to a change of amino acid 3 from Leu to Phe. This substitution is stably associated with the persistent phenotype throughout multiple passages in different cell lines and eggs and cannot be found in any other influenza C viruses.