The Genome-linked Protein of Cherry Leaf Roll Virus

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Abstract
The structures at the 5'' termini of the two genomic RNAa species of cherry leaf roll virus (CLRV) were found to be neither 7-methylguanosine caps, nor 5''-hydroxyl groups or 5''-phosphate groups. CLRV RNA could be iodinated using Na125I and Iodogen; the labelled moiety appeared to be covalently linked to the RNA and could be removed by treatment with Pronase or proteinase K without altering the electrophoretic mobility of the RNA. The infectivity of RNA was greatly diminished by these enzymes, but such treatment impaired neither the fidelity nor the efficiency of translation of the RNA in vitro. Electrophoresis of the acetone-precipitable material released from the RNA by ribonuclease A treatment yielded a single radioactive component corresponding in mobility to a protein with a mol. wt. of about 3500. This molecule (VPg) presumably corresponds to the protease-sensitive structure needed for infectivity. An antiserum prepared against RNA of the birch isolate of CLRV precipitated homologous VPg as well as those of the rhubarb, dogwood, walnut and Sambucus racemosa isolates of CLRV, but not the VPgs of arabis mosaic nepovirus or tomato black ring nepovirus.