“…It remains to be determined whether the attenuated biological behaviour of PMMV-S in tobacco, in comparison with TMV and ToMV, could be ascribed to regions of maximum sequence heterogeneity or to segments of the non-highly conserved sequence of the 126K/183K protein, as previously described for the attenuated L11A strain ofToMV (Nishiguchi et al, 1985) in which the amino acid substitutions responsible for this characteristic have been mapped in regions, not highly conserved, of the 126K protein (amino acid residues 348, 759 and 894). It is also unknown whether the ability of PMMV-S to break the resistance against tobamoviruses conferred by the E 1 and L 2 genes in pepper (Boukema et al, 1980;Garcia-Luque et al, 1990) is due to any of the amino acid changes which take place in this protein, as described for the Ltal strain of ToMV, in which two amino acid substitutions (Glu to Gin and Tyr to His) at positions 979 and 984, respectively (980 and 985 in the PMMV-S protein) have been identified as those responsible for the ability of this strain to break the Tm-l resistance gene in tomato .…”