title: The nucleotide sequence and genome organization of Sclerophthora macrospora virus A.
abstract: Sclerophthora macrospora virus A (SmV A) found in S. macrospora, the pathogenic fungus responsible for downy mildew of gramineous plants, is a small icosahedral virus containing three segments (RNAs 1, 2, and 3) of the positive-strand ssRNA genome. In the present study we report the complete nucleotide sequence of the SmV A genome. The viral genome RNA 1 consists of 2928 nucleotides (nt) and has two open reading frames (ORFs 1a and 1b). ORF 1a contains the motifs of RNA-directed RNA polymerase (RdRp). The function of ORF 1b is unknown. RNA 2 consists of 1981 nt and single ORF (ORF 2). ORF 2 encodes a capsid protein. RNA 3 consists of 977 nt but not any ORFs, suggesting it as a satellite RNA. The deduced amino acid sequence of ORF 1a shows some similarity to those of RdRp of certain positive-strand RNA viruses, especially to the members of the family Nodaviridae, and that of ORF 2 to CP of the members in the family Tombusviridae. The nucleotide sequence of RNA 3 shows a 40-nucleotide length of partial similarity to S. macrospora virus B (SmV B) RNA. The capsid of SmV A is composed of two capsid proteins, CP 1 (p43) and CP 2 (p39), both encoded in ORF 2. CP 2 is apparently derived from CP 1 via proteolytic cleavage at the N-terminus. The genome organization of SmV A is characteristic and distinct from those of other known fungal RNA viruses, including SmV B. These results suggest that SmV A should be classified into a new group of mycoviruses.
authors.affiliation: Laboratory of Plant Pathology, Department of Agricultural and Environmental Biology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Yokoi
authors.forename: Shuichi
authors.initials: S
authors.lastname: Yamashita
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Hibi
mesh_terms: D000595:Amino Acid Sequence; D002213:Capsid / Q000737:chemistry; D005658:Fungi / Q000821:virology*; D016679:Genome, Viral; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D012275:Oryza / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology; D012328:RNA Viruses / Q000145:classification / Q000235:genetics*; D012367:RNA, Viral / Q000235:genetics*; D017423:Sequence Analysis, RNA; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D012367:RNA, Viral; D014764:Viral Proteins