The non-structural leader protein gene of foot-and-mouth disease virus is highly variable between serotypes

Aphthoviruses are unique among picornaviruses in that they alone encode a f unctional L proteinase as the first component of the viral polyprotein. The L genes of a few Indian foot-and-mouth disease viruses were sequenced and compared with those available to study the extent of variation in this gene . Besides the two in-frame start codons present in all FMDV L genes, the As ia-I vaccine virus had an additional in-frame AUG (start) codon, at codon p osition 3. Amino acid sequence comparison revealed that 39.8% of positions were capable of accepting replacements, yet the residues of the catalytic d yad were totally conserved. Sequence comparison at the C-terminus of the pr otein indicated that K/R down arrow GAGQS is sufficient for L/P1 cleavage. Phylogenetic analysis based on the L gene sequences did not reveal any sero type-specific clustering. The probable implications of the observed high va riability in this non-structural gene is briefly discussed.