NUCLEOTIDE-SEQUENCES OF THE NEURAMINIDASE GENES OF INFLUENZA A LENINGRAD/L34/57 (H2N2) VIRUS AND 2 OF ITS LIVE, ATTENUATED, COLD-ADAPTED VARIANTS/

The nucleotide sequences of the neuraminidase (NA) genes of the A/Leni ngrad/134/57 (H2N2) wild-type (Len/wt) virus as well as two of its liv e attenuated, cold-adapted (ca) variants, A/Leningrad/ 134/17/57 (Len/ 17) and A/Leningrad/134/47/57 (Len/47), were determined. In comparison with Len/wt, one nucleotide change (C-225 to A) was found in the NA g ene of Len/17. This change codes for a Thr-to-Asn substitution at posi tion 69 of NA. The NA gene of the more attenuated Len/47 ca virus has one silent (T-814 to C) and two coding nucleotide substitutions, C-78 to T (Ala-20 to Val) and C-225 to A (Thr-69 to Asn), These sequence da ta were used to design a PCR-restriction technique to determine the or igin of the NA gene in candidate live, attenuated vaccine reassortants made by reassorting these ca strains with current field viruses.