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Ribonucleic acid (RNA) is a molecule that is present in the majority of living organisms and viruses. It is made up of nucleotides, which are ribose sugars attached to nitrogenous bases and phosphate groups. The nitrogenous bases include adenine, guanine, uracil, and cytosine. RNA mostly exists in the single-stranded form, but there are special RNA viruses that are double-stranded. The RNA molecule can have a variety of lengths and structures. An RNA virus uses RNA instead of DNA as its genetic material and can cause many human diseases. Transcription is the process of RNA formation from DNA, and translation is the process of protein synthesis from RNA. The means of RNA synthesis and the way that it functions differs between eukaryotes and prokaryotes. Specific RNA molecules also regulate gene expression and have the potential to serve as therapeutic agents in human diseases.

RNA viruses can survive and disrupt physiological processes by replicating their genome inside a host cell. There are different kinds of RNA viruses, and each has a unique mechanism of replication. Double-stranded RNA viruses, such as retroviruses, fuse with host cell membranes and inject their viral contents inside to replicate their genome via reverse transcription. Reverse transcription requires a ribonuclease H and a DNA polymerase with the ability to copy an RNA or a DNA template to synthesize a linear double-stranded DNA from an RNA.[19] Positive-stranded RNA viruses have a positive virion RNA that already acts as an mRNA and, therefore, can be translated immediately by RNA polymerase. Negative-stranded RNA viruses have a negative virion RNA that is complementary to mRNA and must be copied into a positive-sense mRNA before translation. Viral proteins are then released from the host cell to infect other cells, consequently interfering with normal biological processes. Many neurological diseases such as spinocerebellar ataxia (SCA), amyotrophic lateral sclerosis (ALS), myotonic dystrophy, frontotemporal dementia (FTD), fragile X tremor/ataxia syndrome (FXTAS) and Huntington's disease-like 2 (HDL-2), etc., are attributed to the expansion of non-coding RNA repeats. The repeat expansion generates abnormal hairpin folds to develop in an RNA strand, thus disrupting the normal RNA function. Accumulation of such RNA within the nucleus is termed RNA toxicity, which can induce splicing defects, nucleolar functional abnormality, cytoplasmic and mRNA transport, and autophagy.[20]