Kazakh strains of tobacco mosaic virus: two strains with potentially destabilizing amino acid substitutions in the coat protein

Abstract

Some properties of two Kazakh strains (K1 and K2) of tobacco mosaic virus (TMV) are described. K1 had been isolated by Dr M. Gol'din in 1963, and K2 recently in our laboratory. Both strains were rather similar in host range and antigenic properties to the tomato strain of TMV (tomato mosaic virus, ToMV), but differed from the latter by inducing unusual symptoms on upper noninoculated leaves of infected tobacco plants. K1 was semi-defective and temperature-sensitive, and formed large amounts of long RNA-free helical protein rods in infected plants. K2 was found to be neither defective nor temperature-sensitive, and did not produce protein rods in infected cells. K1 and K2 coat protein gene sequencing data showed, as expected, that both proteins are similar in primary structure to ToMV coat protein: only three amino acid substitutions, relative to ToMV, were found in K1 and five in K2 coat protein. Two of these substitutions are unusual, namely, substitution of normally strictly conserved R92 by S (with concomitant Q99→R change) in K2 and substitution of K53 by E in K1.