Viroids are the smallest infectious pathogens known. They are composed solely of a short strand of circular, single-stranded RNA that has no protein coating. All known viroids are inhabitants of higher plants, in which most cause diseases, ranging in economic importance.
Theodor Otto Diener is the Swiss-American plant pathologist who, in 1971, discovered that the causative agent of the potato spindle tuber disease is not a virus, but a novel agent, which consists solely of a short strand of single-stranded RNA without a protein capsid, eighty times smaller than the smallest viruses. He proposed to name it and similar agents to be discovered viroids. Viroids displace viruses as the smallest infectious agents known.
Pospiviroid is a genus of viroid which most commonly infects tubers. It belongs to the family pospiviroidae. The first viroid discovered was a pospiviroid, the PSTVd species.
The Pospiviroidae are a family of viroids, including the first viroid to be discovered, PSTVd. Their secondary structure is key to their biological activity. The classification of this family is based on differences in the conserved central region sequence. The genome consists of an LH terminal domain, a pathogenic domain, conserved central domain, variable domain, and an RH terminal domain. Pospiviroidae replication occurs in an asymmetric fashion via host cell RNA polymerase, RNase, and RNA ligase.
Crinivirus, formerly the lettuce infectious yellows virus group, is a genus of viruses, in the family Closteroviridae. They are linear, single-stranded positive sense RNA viruses. There are currently 13 species in this genus including the type species Lettuce infectious yellows virus. Diseases associated with this genus include: yellowing and necrosis, particularly affecting the phloem.
The Alfalfa mosaic virus (AMV) coat protein binding (CPB) RNA is an RNA element which is found in the 3' UTR of the genome. AMV CPB can stimulate the translation of AMV RNA by between 50 and 100-fold. This family contains at least two coat protein binding sites which are thought to be essential for efficient RNA translation.
The Alfalfa mosaic virus RNA 1 5' UTR stem-loop represents a putative stem-loop structure found in the 5' UTR in RNA 1 of alfalfa mosaic virus. RNA 1 is responsible for encoding the viral replicase protein P1. This family is required for negative strand RNA synthesis in the alfalfa mosaic virus and may also be involved in positive strand RNA synthesis.
The Coronavirus 3' stem-loop II-like motif is a secondary structure motif identified in the 3'untranslated region (3'UTR) of astrovirus, coronavirus and equine rhinovirus genomes. Its function is unknown, but various viral 3' UTR regions have been found to play roles in viral replication and packaging.
The Coronavirus 3' UTR pseudoknot is an RNA structure found in the coronavirus genome. Coronaviruses contain 30 kb single-stranded positive-sense RNA genomes. The 3' UTR region of these coronavirus genomes contains a conserved ~55 nucleotide pseudoknot structure which is necessary for viral genome replication. The mechanism of cis-regulation is unclear, but this element is postulated to function in the plus-strand.
In molecular biology, the coronavirus frameshifting stimulation element is a conserved stem-loop of RNA found in coronaviruses that can promote ribosomal frameshifting. Such RNA molecules interact with a downstream region to form a pseudoknot structure; the region varies according to the virus but pseudoknot formation is known to stimulate frameshifting. In the classical situation, a sequence 32 nucleotides downstream of the stem is complementary to part of the loop. In other coronaviruses, however, another stem-loop structure around 150 nucleotides downstream can interact with members of this family to form kissing stem-loops and stimulate frameshifting.
Interferon gamma 5' UTR regulatory elements are a family of regulatory RNAs. This family represents a pseudoknot containing stem-loop structure found in the 5' UTR of interferon-gamma mRNA. This structure is thought to be involved in translational regulation and the pseudoknot has been found to activate protein kinase R (PKR) which is known to be a translational inhibitor. Mutations in the pseudoknot structure have been found to reduce PKR activation and increase the translation of interferon-gamma.
Retroviral Psi packaging element is a cis-acting RNA element identified in the genomes of the retroviruses Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV). It is involved in regulating the essential process of packaging the retroviral RNA genome into the viral capsid during replication. The final virion contains a dimer of two identical unspliced copies of the viral genome.
The histone 3' UTR stem-loop is an RNA element involved in nucleocytoplasmic transport of the histone mRNAs, and in the regulation of stability and of translation efficiency in the cytoplasm. The mRNAs of metazoan histone genes lack polyadenylation and a poly-A tail, instead 3' end processing occurs at a site between this highly conserved stem-loop and a purine rich region around 20 nucleotides downstream. The stem-loop is bound by a 31 kDa stem-loop binding protein. Together with U7 snRNA binding of the HDE, SLBP binding nucleates the formation of the processing complex.
Hepatitis C alternative reading frame stem-loop is a conserved secondary structure motif identified in the RNA genome of the Hepatitis C virus (HCV) which is proposed to have an important role in regulating translation and repression of the viral genome.
V-snoRNA1 is a box CD-snoRNA identified in B lymphocytes infected with the Epstein–Barr virus. This snoRNA is the first known example of a snoRNA expressed from a viral genome. It is homologous to eukaryotic snoRNAs because it contains the C and D boxes sequence motifs but lacks a terminal stem-loop structure. The nucleolar localization of v-snoRNA1 was determined by in situ hybridization. V-snoRNA1 can form into a ribonucleoprotein complex (snoRNP) as co-immunoprecipitation (CoIP) assays showed that this snoRNA interacts with the snoRNA core proteins, fibrillarin, Nop56, Nop58. It has also been proposed that this snoRNA may act as a miRNA-like precursor that is processed into 24-nucleotide-sized RNA fragments that target the 3'UTR of viral DNA polymerase mRNA.
The Chlorobi-RRM RNA motif is a conserved RNA structure identified by bioinformatics. It is found within bacteria in the phylum Chlorobi, and is exclusively detected in the presumed 5' untranslated regions of genes that encode putative RNA-binding proteins. Since many RNA-binding proteins regulate their own expression in a feedback mechanism by binding or acting up their 5' UTR, it was proposed that the Chlorobi-RRM is a component in an analogous feedback mechanism. Structurally, the motif consists of two stem-loops, the second of which might function as a rho-independent transcription terminator.
The Cyano-2 RNA motif is a conserved RNA structure identified by bioinformatics. Cyano-2 RNAs are found in Cyanobacterial species classified within the genus Synechococcus. Many terminal loops in the two conserved stem-loops contain the nucleotide sequence GCGA, and these sequences might in some cases form stable GNRA tetraloops. Since the two stem-loops are somewhat distant from one another it is possible that they represent two independent non-coding RNAs that are often or always co-transcribed. The region one thousand base pairs upstream of predicted Cyano-2 RNAs is usually devoid of annotated features such as RNA or protein-coding genes. This absence of annotated genes within one thousand base pairs is relatively unusual within bacteria.
The psaA RNA motif describes a class of RNAs with a common secondary structure. psaA RNAs are exclusively found in locations that presumably correspond to the 5' untranslated regions of operons formed of psaA and psaB genes. For this reason, it was hypothesized that psaA RNAs function as cis-regulatory elements of these genes. The psaAB genes encode proteins that form subunits in the photosystem I structure used for photosynthesis. psaA RNAs have been detected only in cyanobacteria, which is consistent with their association with photosynthesis.
