Coat protein gene sequences of two cucumber mosaic virus strains reveal a single amino acid change correlating with chlorosis induction.

The coat protein genes of two chlorosis-inducing strains of cucumber mosaic virus (CMV) were compared by nucleotide sequence analysis. The predicted amino acid sequences of the encoded coat proteins were compared with those of two other chlorosis-inducing and four mosaic-inducing CMV strains. Overall, the sequences were highly conserved, with more than 95% amino acid sequence identity between any two strains. However, a proline is present at amino acid 129 of all the mosaic-inducing strains, whereas that position is occupied by either a serine or a leucine in the coat proteins of all the chlorosis-inducing strains. The correlation of chlorosis induction and a substitution for proline with leucine or serine at amino acid 129 suggests that this residue is the determinant of chlorosis induction.