Genomic analysis of matrix gene and antigenic studies of its gene product (M1) of a swine influenza virus (H1N1) causing chronic respiratory disease in pigs.

The nucleotide sequence of gene coding for the matrix protein (M1 and M2) of swine influenza (H1N1) virus, A/Sw/Quebec/5393/91 (SwQc91), associated with chronic respiratory disease in pigs, was determined. The deduced amino acid (aa) sequence was compared with the other North American swine strains including the A/Sw/Quebec/192/81 (SwQc81) strain associated with the chronic and acute respiratory disease in pigs. Separate analysis of the M1 and M2 gene products showed different evolutions. M1 had 2 aas changes among 252 aas and these were at positions 4 and 205. The mutation rate was 0.08%, aa changes per residue per year, and its homology with other strains was 99.2%. The M2 protein (97 aas) was relatively more variable than M1 with 5 substitutions. Differences observed were at positions 4, 16, 21, 54 and 95. The mutation rate was 0.51% and its homology with other strains was 94.8%. The M1 gene was cloned in the procaryotic plasmid pET21a and the recombinant plasmid was expressed in Escherichia coli under pre-determined optimal conditions. The recombinant M1 protein (RM1P) (approximately 28 kDa) comigrated as a single band on SDS-PAGE. RM1P was antigenic and reacted with polyclonal sera and 5 monoclonal antibodies (MAbs) spanning 4 epitopes including the membrane binding site and the transcription inhibition activity site. RM1P was immunogenic. The mouse anti-RM1P ELISA antibodies reacted with the purified viral M1 protein and the whole virus.