Characterization of cocksfoot mottle sobemovirus genomic RNA and sequence comparison with related viruses

The genome of cocksfoot mottle virus (CfMV) is a positive-sense ssRNA molecule of 4082 nucleotides as revealed by sequencing the entire genome. The 5'-untranslated region of the genome is 69 nucleotides and the 3'-untranslated region is 225 nucleotides in length. The coding region contains four open reading frames (ORFs). The organization of CfMV ORFs differs significantly from that of the previously sequenced sobemoviruses southern bean mosaic virus and rice yellow mottle virus. ORF1 encodes a protein having a calculated molecular mass of 12.3 kDa. The function of this protein is unknown. The next ORF codes for the putative VPg and serine protease. The ORF2a product consists of 568 amino acids, with a calculated molecular mass of 60.9 kDa. The replicase of CfMV is translated as part of a polyprotein by--1 ribosomal frameshifting in ORF2a. The calculated molecular mass of the transframe protein is 103.4 kDa. ORF3 encodes the 27.6 kDa coat protein. This has been verified by amino acid sequencing of the CfMV coat protein N terminus. Northern blots of total RNA from CfMV-infected barley leaves reveal the 4.1 kb genomic RNA band and one virus-specific band of 1.2 kb, which may represent a subgenomic RNA for coat protein synthesis.