Virology 259, 234-245  (1999)

Symptom Attenuation By A Satellite RNA In Vivo Is Dependent On Reduced Levels of Virus Coat Protein

Jianlong Wang and Anne E. Simon

Department of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003

Many plant RNA viruses provide replication and encapsidation functions for one or more satellite (sat-) RNAs that can modulate the symptoms of the associated helper virus. Sat-RNA C, a virulent sat-RNA associated with turnip crinkle virus (TCV), normally intensifies symptoms but can attenuate symptoms if the TCV coat protein is either replaced with that of cardamine chlorotic fleck carmovirus [Q. Kong, J.-W. Oh, and A. E. Simon (1995) Plant Cell 7, 1625-1634] or if TCV contains an alteration in the coat protein (CP) initiation codon (TCV-CPm) [Q. Kong, J. Wang, and A. E. Simon (1997b) Plant Cell 9, 2051-2063]. To further elucidate the mechanism of symptom attenuation by sat-RNA C, the composition of the CP produced by TCV-CPm (CPCPm) was determined. Our results reveal that CPgp~, likely has two additional amino acids at its N-terminus compared with wild-type TCV CP. TCV-CPm produces reduced levels of CP and this reduction, not the two additional residues at the CP N terminus, is responsible for symptom attenuation by sat-RNA C.