Characterization of the Coat Protein Subgenomic RNA of White Clover Mosaic Virus

Plant Diseases Division, DSIR, Private Bag, Auckland, New Zealand The genomic RNA (6·2 kb) and a 0·9 kb RNA were detected by Northern hybridization in leaves infected with white clover mosaic virus (WC1MV). The 0·9 kb RNA was efficiently encapsidated by one, but not by eight other, isolates of WC1MV. Both RNA species were shown to possess 3'-terminal tracts of poly(A) 200 to 300 nucleotides long by end-labelling with [ 32 P]pCp and digestion with ribonucleases A, Phy M, T 1 and U 2 . The 0·9 kb RNA was mapped to the 3'-terminal region of the genomic RNA using cDNA probes. In rabbit reticulocyte lysates, the 6·2 kb RNA directed predominantly the synthesis of a protein of mol. wt. 160 000 (160K) and several additional proteins. The 0·9 kb RNA directed synthesis of a 25K protein. This protein was shown to be the virus coat protein by its co-migration in gels with the WC1MV coat protein and by its specific immunoprecipitation with antiserum to virus particles. Both RNA species were found in specific association with polysomes indicating that they function as messenger RNAs in infected cells. Received 16 June 1986; accepted 22 September 1986.