[Nucleotide sequence of the RNA polymerase gene attenuated by a variant of foot-and-mouth disease virus and its comparison with the virulence of related variants of subtype A22].

The nucleotide sequence of RNA-polymerase gene and 3'-terminal untranslated genome region of attenuated foot-and-mouth disease virus (FMDV) strain A(22)645 has been determined. RNA-polymerase gene and predicted amino acid sequences of attenuated FMDV strain A(22)645 were compared with those of the original virulent FMDV strain A(22)550. The examined genome region of strain A(22)645 differed from that of strain A(22)550 by 22 nucleotides and 3 amino acids. Three mutations occurred within nucleotide residues 883 to 1026, which encode an extremely conserved amino acid domain corresponding to RNA polymerization and nucleoside triphosphate binding functions. Mutation in 920n caused substitution of conserved amino acid Asn for Ser in the core motif for nucleotide binding Gxxx-TxxxN(S/T). It is possible that change in functional motif caused the alteration of phenotypic virus and loss of pathogenicity for cattle. This may be finally confirmed only after comparative analysis of complete genomes of the examined virus strains.