Purification of the pathogenic RNA (viroid) from exocortis disease has been accomplished. Composition analysis indicates the absence of any DNA or protein and a molar nucleotide composition of CMP, 29.4%; AMP, 21.5%; GMP, 28.8%; and UMP, 19.9%. Even though the AMP UMP and GMP CMP ratios approach unity the per cent hyperchromicity (22%) resembled a tRNA-like molecule and not a dsRNA, while the Tm (52°) in 0.1 SSC was higher than the pure tRNA species tested. Nuclease digestion similarly suggested the presence of a highly ordered structure for the pathogenic RNA. We also introduced low field NMR spectroscopy as a new technique in the study of pathogenic RNA's (viroids) of unknown sequence.
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