title: A chloroplast protein binds a viroid RNA in vivo and facilitates its hammerhead-mediated self-cleavage.
abstract: Viroids, small single-stranded circular RNAs (246-401 nucleotides), do not have mRNA capacity and must recruit host proteins to assist in the steps of their biological cycle. The nature of these cellular factors is poorly understood due to a lack of reliable experimental approaches. Here, to screen for host proteins interacting with viroid RNAs in vivo, we UV-irradiated avocado leaves infected with avocado sunblotch viroid (ASBVd), the type member of chloroplast viroids containing hammerhead ribozymes. This resulted in the detection of several ASBVd-host protein adducts. Tandem mass spectrometry analysis of the most abundant cross-linked species identified the protein component as two closely related chloroplast RNA-binding proteins (PARBP33 and PARBP35) of a family whose members previously have been shown to be involved in stabilization, maturation and editing of chloroplast transcripts. PARBP33 behaves as an RNA chaperone that stimulates in vitro the hammerhead-mediated self-cleavage of the multimeric ASBVd transcripts that result from rolling circle replication, indicating that this reaction, despite its RNA-based mechanism, is facilitated by proteins. The structural and functional parallelism between PARBP33 and PARBP35, and some proteins involved in viral RNA replication, indicates that viroids and RNA viruses recruit similar host proteins for their replication.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas (UPV-CSIC), Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, Valencia 46022, Spain.
authors.forename: José-Antonio
authors.initials: JA
authors.lastname: Daròs
authors.forename: Ricardo
authors.initials: R
authors.lastname: Flores
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000378:metabolism*; D017931:DNA Primers; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000378:metabolism*; D010942:Plant Viruses / Q000235:genetics*; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D010940:Plant Proteins; D012333:RNA, Messenger; D012367:RNA, Viral