Comparative study on genomes of two Japanese melon necrotic spot virus isolates

Nucleotide sequences of the genomes of two Japanese Melon necrotic spot virus (MNSV) isolates, NH and NK were determined. The open reading frames (ORFs) in both genomes encode five proteins: p29 (the pre-readthrough domain of p89), p89 (the readthrough domain of p89 identified as the putative RNA-dependent RNA polymerase), p14 (the pre-readthrough domain of p7A), p7A (the putative movement protein), and p42 (coat protein, CP). Nucleotide and amino acid sequence identities of the five proteins of NH and NK isolates were estimated at 97.4-99.5% and 97.7-100%, respectively. NK isolate but not NH isolate infected systemically leaves of Cucumis melo plants. When deduced amino acid sequences of p7A proteins of NH and NK isolates were compared, only one difference at position 16 (serine in NH isolate and isoleucine in NK isolate) was observed. p7A protein is considered the putative movement protein. The serine of p7A protein of NH isolates may be involved in systemic infection. In addition, phylogenetic relationships of genes based on nucleotide sequences revealed that NH and NK isolates might form a group, and S isolate, serologically different from NH and NK isolates, might represent a distinct isolate not belonging to this group.