From Wikipedia, the free encyclopedia
Jump to: navigation, search
Scientific classification
Order: Unassigned
Family: Avsunviroidae

The Avsunviroidae are a family of viroids. At present three members are known. They consist of RNA genomes between 246-375 nucleotides in length. They are single-stranded covalent circles and have intramolecular base pairing. All members lack a central conserved region.


Replication occurs in the chloroplasts of plant cells. Key features of replication include no helper virus required and no proteins are encoded for. Unlike the other family of viroids, Pospiviroidae, Avsunviroidae are thought to replicate via a symmetrical rolling mechanism. It is thought the positive RNA strand acts as a template to form negative strands with the help of an enzyme thought to be RNA polymerse plus 3 II. The negative RNA strands are then cleaved by ribozyme activity and circularises. A second rolling circle mechanism forms a positive strand which is also cleaved by ribozyme activity and then ligated to become circular. The site of replication is unknown but it is thought to be in the chloroplast and in the presence of Mg2+ ions.


Predictions of structure have suggested that they exist either as rod-shaped molecules with regions of base pairing causing formation of some hair pin loops or have branched configurations.


The family has three genera, with a total of four species.