title: Asp-->Asn substitutions in the putative calcium-binding site of the turnip crinkle virus coat protein affect virus movement in plants.
abstract: Many plant virus coat proteins have binding sites for divalent cations, particularly calcium. It has been speculated that the purpose of such sites is to ensure that plant viruses release their RNA only in the host cytoplasm which has a low calcium concentration. By comparison to tomato bushy stunt virus, two of the amino acids that probably interact directly with calcium ions in turnip crinkle virus (TCV) capsids, Asp155 and Asp157, were substituted with Asn residues by oligonucleotide-directed mutagenesis to create the mutant TCV-M18. TCV-M18 coat protein, and virions accumulated to wild-type levels in isolated protoplasts. Mutant virions were able to uncoat and to initiate de novo replication in protoplasts although no symptoms were observed in plants inoculated with TCV-M18. Mutant RNA accumulated to much lower levels than wild-type RNA in inoculated leaves and was not detected in upper, uninoculated leaves. The lower infectivity of TCV-M18 in plants may be due to a decreased capacity to move efficiently from cell to cell, and we suggest the possibility that TCV coat protein plays an active, pivotal role in cell-to-cell movement interactions.
authors.affiliation: Department of Plant Pathology, Kansas State University, Manhattan 66506-5502.
authors.forename: M M
authors.initials: MM
authors.lastname: Laakso
authors.forename: L A
authors.initials: LA
authors.lastname: Heaton
mesh_terms: D001216:Asparagine / Q000235:genetics; D001224:Aspartic Acid / Q000235:genetics; D001483:Base Sequence; D001692:Biological Transport; D001937:Brassica / Q000382:microbiology*; D002118:Calcium / Q000378:metabolism*; D002213:Capsid / Q000235:genetics*; D008969:Molecular Sequence Data; D053830:Plant Viral Movement Proteins; D010942:Plant Viruses / Q000235:genetics* / Q000378:metabolism; D012328:RNA Viruses / Q000235:genetics* / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D053830:Plant Viral Movement Proteins; D014764:Viral Proteins; D001224:Aspartic Acid; D001216:Asparagine; D002118:Calcium