Next Article in Journal
A(H5N1) Virus Evolution in South East Asia
Next Article in Special Issue
Hepatitis Delta Virus RNA Replication
Previous Article in Journal / Special Issue
Viroid Pathogenicity: One Process, Many Faces
Article Menu

Export Article

Open AccessReview
Viruses 2009, 1(2), 317-334;

Viroid Replication: Rolling-Circles, Enzymes and Ribozymes

Instituto de Biología Molecular y Celular de Plantas (UPV-CSIC), Avenida de los Naranjos s/n, 46022 Valencia, Spain
Author to whom correspondence should be addressed.
Received: 6 July 2009 / Revised: 9 September 2009 / Accepted: 9 September 2009 / Published: 14 September 2009
(This article belongs to the Special Issue Subviral RNAs)
Full-Text   |   PDF [427 KB, uploaded 12 May 2015]   |  


Viroids, due to their small size and lack of protein-coding capacity, must rely essentially on their hosts for replication. Intriguingly, viroids have evolved the ability to replicate in two cellular organella, the nucleus (family Pospiviroidae) and the chloroplast (family Avsunviroidae). Viroid replication proceeds through an RNA-based rolling-circle mechanism with three steps that, with some variations, operate in both polarity strands: i) synthesis of longer-than-unit strands catalyzed by either the nuclear RNA polymerase II or a nuclear-encoded chloroplastic RNA polymerase, in both instances redirected to transcribe RNA templates, ii) cleavage to unit-length, which in the family Avsunviroidae is mediated by hammerhead ribozymes embedded in both polarity strands, while in the family Pospiviroidae the oligomeric RNAs provide the proper conformation but not the catalytic activity, and iii) circularization. The host RNA polymerases, most likely assisted by additional host proteins, start transcription from specific sites, thus implying the existence of viroid promoters. Cleavage and ligation in the family Pospiviroidae is probably catalyzed by an RNase III-like enzyme and an RNA ligase able to circularize the resulting 5’ and 3’ termini. Whether a chloroplastic RNA ligase mediates circularization in the family Avsunviroidae, or this reaction is autocatalytic, remains an open issue. View Full-Text
Keywords: viroids; catalytic RNAs; hammerhead ribozymes viroids; catalytic RNAs; hammerhead ribozymes

Figure 1

This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

Share & Cite This Article

MDPI and ACS Style

Flores, R.; Gas, M.-E.; Molina-Serrano, D.; Nohales, M.-Á.; Carbonell, A.; Gago, S.; De la Peña, M.; Daròs, J.-A. Viroid Replication: Rolling-Circles, Enzymes and Ribozymes. Viruses 2009, 1, 317-334.

Show more citation formats Show less citations formats

Related Articles

Article Metrics

Article Access Statistics



[Return to top]
Viruses EISSN 1999-4915 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top