Homologous sequences in non-structural proteins from cowpea mosaic virus and picornaviruses

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Abstract
Computer analyses have revealed sequence homology between two non‐structural proteins encoded by cowpea mosaic virus (CPMV), and corresponding proteins encoded by two picornaviruses, poliovirus and foot‐and‐mouth disease virus. A region of 535 amino acids in the 87‐K polypeptide from CPMV was found to be homologous to the RNA‐dependent RNA polymerases from both picornaviruses, the best matches being found where the picornaviral proteins most resemble each other. Additionally, the 58‐K polypeptide from CPMV and polypeptide P2‐X from poliovirus contain a conserved region of 143 amino acids. Based on the homology observed, a genetic map of the CPMV genome has been constructed in which the 87‐K polypeptide represents the core polymerase domain of the CPMV replicase. These results have implications for the evolution of RNA viruses, and mechanisms are discussed which may explain the existence of homology between picornaviruses (animal viruses with single genomic RNAs) and comoviruses (plant viruses with two genomic RNAs).