Viroids are single-stranded covalently closed circular RNA molecules existing as highly base-paired rod-like structures.

TLDR

Viroids are uncoated infectious RNA molecules pathogenic to certain higher plants. Four different highly purified viroids were studied. The study determined that cucumber pale fruit viroid, citrus exocortis viroid from Gynura and tomato, and potato spindle tuber viroid have molecular weights of 110,000–127,000, are single‑stranded, covalently closed circular RNAs, and form highly stable, self‑complementary rod‑like structures.

Abstract

Viroids are uncoated infectious RNA molecules pathogenic to certain higher plants. Four different highly purified viroids were studied. By ultracentrifugation, thermal denaturation, electron microscopy, and end group analysis the following features were established: (i) the molecular weight of cucumber pale fruit viroid from tomato is 110,000, of citrus exocortis viroid from Gynura 119,000, of citrus exocortis viroid from tomato 119,000 and of potato spindle tuber viroid from tomato 127,000. (ii) Viroids are single-stranded molecules. (iii) Virods exhibit high thermal stability, cooperativity, and self-complementarity resulting in a rod-like native structure. (iv) Viroids are covalently closed circular RNA molecules.