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

The 3'-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 M(r) of 36,229. 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 (GNNTNTNTSNT) 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 coli 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.