title: Rolling-circle replication of viroids, viroid-like satellite RNAs and hepatitis delta virus: variations on a theme.
abstract: Viroids and viroid-like satellite RNAs from plants, and the human hepatitis delta virus (HDV) RNA share some properties that include small size, circularity and replication through a rolling-circle mechanism. Replication occurs in different cell compartments (nucleus, chloroplast and membrane-associated cytoplasmatic vesicles) and has three steps: RNA polymerization, cleavage and ligation. The first step generates oligomeric RNAs that result from the reiterative transcription of the circular templates of one or both polarities, and is catalyzed by either the RNA-dependent RNA polymerase of the helper virus on which viroid-like satellite RNAs are functionally dependent, or by host DNA-dependent RNA polymerases that, remarkably, viroids and HDV redirect to transcribe RNA templates. Cleavage is mediated by host enzymes in certain viroids and viroid-like satellite RNAs, while in others and in HDV is mediated by cis-acting ribozymes of three classes. Ligation appears to be catalyzed mainly by host enzymes. Replication most likely also involves many other non-catalytic proteins of host origin and, in HDV, the single virus-encoded protein.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas (UPV-CSIC), Campus Universidad Politécnica, Avenida de los Naranjos, Valencia, Spain. rflores@ibmcp.upv.es
authors.forename: Ricardo
authors.initials: R
authors.lastname: Flores
authors.forename: Douglas
authors.initials: D
authors.lastname: Grubb
authors.forename: Amine
authors.initials: A
authors.lastname: Elleuch
authors.forename: María-Ángeles
authors.initials: MÁ
authors.lastname: Nohales
authors.forename: Sonia
authors.initials: S
authors.lastname: Delgado
authors.forename: Selma
authors.initials: S
authors.lastname: Gago
mesh_terms: D000818:Animals; D003698:Hepatitis Delta Virus / Q000235:genetics* / Q000502:physiology; D019244:RNA, Satellite / Q000235:genetics*; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D014772:Viroids / Q000235:genetics*; D014779:Virus Replication
chemical_list: D019244:RNA, Satellite; D012367:RNA, Viral