Coat protein of potyviruses

Abstract

The amino acid sequence of the coat protein of the Johnsongrass (JG) strain of sugarcane mosaic virus (SCMV) has been determined by protein sequencing techniques. The protein contains 303 amino acid residues corresponding to a molecular weight of 33,510 and when compared to the coat proteins of other potyviruses that have been characterized (263–267 residues) is found to have additional residues at its N-terminus. The N-terminus is acetylated as shown by fast atom bombardment mass spectrometry. Partial amino acid sequences of the coat proteins of the other three Australian SCMV strains, sugarcane (SC), Queensland blue couch grass (BC) and sabi grass (Sabi) have also been obtained. The sequence data and the comparative tryptic peptide HPLC profiles showed that the JG coat protein was substantially different from those of the other three SCMV strains, the sequence homology being around 66 per cent. This is in marked contrast to the high sequence homology between SC, BC and Sabi strains (95–100 per cent) but similar to that (51–62 per cent) found between coat proteins of distinct members of the potyvirus group. On the basis of these structural findings and other information on major differences in serological, biological and biochemical properties we believe that the present JG strain should not be considered a strain of SCMV but should be regarded as an independent member of the potyvirus group. The name “Johnsongrass mosaic virus” is proposed for this new member.