Diener T O
Natl Cancer Inst Monogr. 1982;60:161-7.
Viroids are nucleic acid species of low molecular weight and unique structure that cause several important diseases of cultivated plants. Viroids are the smallest known agents of infectious disease. Unlike viral nucleic acids, viroids are not encapsidated. Despite their small size, viroids replicate autonomously in cells of susceptible plant species. Known viroids are single-stranded, covalently closed, circular, as well as linear, RNA molecules with extensive regions of intramolecular complementarity; they exist in their native state as highly base-paired rods. The biological properties of viroids are determined by their primary structures; viroids thus constitute genetic systems of minimal complexity. So far, viroids have been identified only as pathogens of higher plants, but it is likely that certain animal (including human) diseases are caused by similar agents.
类病毒是低分子量且结构独特的核酸种类，可引发多种重要的栽培植物疾病。类病毒是已知最小的传染病原体。与病毒核酸不同，类病毒没有衣壳包裹。尽管类病毒体积小，但它们能在易感植物物种的细胞中自主复制。已知的类病毒是单链、共价闭合的环状以及线性RNA分子，具有广泛的分子内互补区域；它们以高度碱基配对的棒状形式以天然状态存在。类病毒的生物学特性由其一级结构决定；因此，类病毒构成了复杂性最低的遗传系统。到目前为止，类病毒仅被鉴定为高等植物的病原体，但某些动物（包括人类）疾病很可能是由类似病原体引起的。
