Unusual amino-terminal sequence repeat characterizes the capsid protein of dasheen mosaic potyvirus

Abstract

The T-terminal region of a Florida isolate of dasheen mosaic potyvirus (DMV-LA) genome including the coat protein (CP) gene was cloned and sequenced. Protease digestion was predicted to occur between the glutamine and alanine residues at positions 79 and 80 of the 408 residue long polypeptide to produce a CP of 329 amino acids with an estimated 3//,. of 36229. Following the putative protease recognition site is a DAG sequence, which is conserved among aphid-transmitted potyviral CPs. There is an unusual and unique stretch of 52 amino acids after the DAG that is repetitive and rich in threonine and asparagine. A sequence of 10 residues (GNNTNTNT2T) was repeated three times in tandem within this stretch and was followed by six proline residues. Several potential glycosylation sites were found clustered within this region. Expression in Escherichia co//and Western blotting of the CP confirmed its size and serological identity. Sequence comparisons and phylogenetic reconstructions indicated that DMV is a distinct potyvirus within the passionfruit woodiness virus subgroup cluster.

Molecular characterization of dasheen mosaic virus isolates infecting edible aroids in India

“…Protease cleavage sites in potyvirus polyprotein sequences for the production of the CP are Q/A, Q/S or Q/G residues (Pappu et al, 1994). DsMV-Amp1, DsMVTa1 and DsMV-Xan1 have the potential protease cleavage site at position 7 and 8, between Q/A to produce a CP of 313 amino acids (Fig.…”

“…Partial sequence characterization of DsMV infecting Colocasia (Pappu et al,1994), Xanthosoma (Reyes et al, 2009) and Zantedeschia (Chen et al, 2001) and complete genome sequence from Zantedeschia have been reported (Chen et al, 2001). However no sequence information of DsMV from A. paeoniifolius, C. esculenta, and X. sagittifolium in India has so far been reported.…”

Replication slippage in the evolution of potyviruses

“…Evidence has been presented recently that unequal recombination within the genome has contributed to the evolution of the coat protein of dasheen mosaic potyvirus (Pappu et al, 1994). It has also been found that differences in length of the N-terminal portion of the coat protein of different potyvirus species result from repetitions that are up to 17 amino acids in length (Ward et al, 1995).…”

“…Repetition of a sequence unit of this size is unlikely to have arisen by slippage (Levinson & Gutman, 1987) and, in eukaryotes, would be most likely to have arisen by unequal crossingover. Thus, it seems possible that the sequence is evidence of intragenomic recombination in potyviruses (Pappu et al, 1994). However, the repetitive sequence region of dasheen mosaic virus extends beyond this region of tandem repetition and the individual repeats themselves are internally repetitious.…”

“…The repetitive sequence in the N-terminal region of the dasheen mosaic virus coat protein comprises, in part, three tandemly arrayed imperfect repeats of a 10 amino acid (30 base) unit (Pappu et al, 1994). Repetition of a sequence unit of this size is unlikely to have arisen by slippage (Levinson & Gutman, 1987) and, in eukaryotes, would be most likely to have arisen by unequal crossingover.…”