Physical properties of a minimal infectious RNA (viroid) associated with the exocortis disease

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 AMPUMP and GMPCMP 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.