Partial Cleavage of Sweet Potato Feathery Mottle Virus Coat Protein Subunit by an Enzyme in Extracts of Infected Symptomless Leaves

Abstract

SUMMARYThe coat protein of particles of sweet potato feathery mottle potyvirus (SPFMV) extracted from Ipomoea spp. migrated in SDS-PAGE mainly as bands of Mr 38000 (38K), 36K, 32K and 30K. Trypsin treatment of the particles resulted in the appearance of only one 30K polypeptide. The inclusion of protease inhibitors in the extraction procedure did not alter the heterogeneity of SPFMV coat protein. A partially purified fraction of extracts from recovering, symptomless, but not from healthy leaves of L nil had a proteolytic activity similar to that of trypsin. Amino acid sequencing showed that the trypsin-cleaved 30K polypeptide had some sequence homology with other potyvirus coat proteins. The site at which the lpomea extract cleaved the protein was five amino acids nearer the N terminus than the trypsin cleavage site.

Comparison of the capsid protein cistron from serologically distinct strains of sweetpotato feathery mottle virus (SPFMV)

“…This sequence is located 80 residues from the predicted N terminus of the capsid protein (Fig. 3) very close to the position estimated by Salomon [19] (+ 70 from the N terminus).…”

“…The N-terminus of trypsin-resistant potyviral capsid protein is another common motif in potyviruses [ 19]. A perfect alignment was found between the previously determined amino acid sequence of SPFMV (D-VNVGTVGTF) from a trypsin-treated capsid protein [ 19] and our SPFMV-RC predicted amino acid sequence. This sequence is located 80 residues from the predicted N terminus of the capsid protein (Fig.…”

Potyvirus serology, sequences and biology

“…Results obtained by Salomon [44] with SPFMV suggest that the termini may have a role in virus replication or systemic movement. A proteolytic activity was induced in SPFMV-infected sweet potato and morning glory, even in leaves without detectable virus, but not in healthy plants, and this activity may contribute to the attenuation of symptoms and ultimate recovery from virus upon further growth [44].…”

“…Results obtained by Salomon [44] with SPFMV suggest that the termini may have a role in virus replication or systemic movement. A proteolytic activity was induced in SPFMV-infected sweet potato and morning glory, even in leaves without detectable virus, but not in healthy plants, and this activity may contribute to the attenuation of symptoms and ultimate recovery from virus upon further growth [44]. However, the proteolytic activity in sweet potato may affect viral gene products and processes other than CP, so this is not clear evidence for a role of the N-terminus in movement apart from its important role in aphid transmission [3,4] which is discussed elsewhere in this volume.…”

Nucleotide Sequence at the 3′-Terminal Region of Sweet Potato Feathery Mottle Virus (Ordinary Strain, SPFMV-O) RNA

“…Underlined region coincides with the 10 amino acid sequence of a peptide derived from trypsin-treated coat protein of SPFMV isolated in Israel. 6 ) Asterisks below the amino acids indicate the consensus amino acids for RNA polymerase of RNA viruses.?) Arrows below nucleotide sequence indicate the inverted repeat (see Fig.…”