Nucleotide sequences of the neuraminidase genes of influenza A/Leningrad/134/57 (H2N2) virus and two of its live, attenuated, cold-adapted variants.

The nucleotide sequences of the neuraminidase (NA) genes of the A/Leningrad/134/57 (H2N2) wild-type (Len/wt) virus as well as two of its live 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 gene of Len/17. This change codes for a Thr-to-Asn substitution at position 69 of NA.

[The NS gene--a possible determinant of apathogenicity of a cold-adapted donor of attenuation A /Leningrad/134/47/57 and its reassortants].

Phenotypical properties of single-gene reassortants of attenuated cold-adapted strain A/Leningrad/135/47/57 (H2N2) and strain A/PR8/34 virulent for laboratory animals were studied. Only the group of reassortants inheriting NS gene from cold-adapted virus was fully attenuated for various animals species, similarly as reassortants with 6/2 genomic formula containing all the 6 internal protein genes from strain A/Leningrad/134/47/57. Reassortant 25A-1 single-gene for NS was temperature-sensitive (ts) on mammalian cells but formed plaques at 40 degrees C on chicken kidney cells.