VS ribozyme

The Varkud satellite (VS) ribozyme is an RNA enzyme that carries out the cleavage of a phosphodiester bond.

Varkud satellite (VS) ribozyme is the largest known nucleolyic ribozyme and found to be embedded in VS RNA. VS RNA is a long non-coding RNA exists as a satellite RNA and is found in mitochondria of Varkud-1C and few other strains of Neurospora. VS ribozyme contains features of both catalytic RNAs and group 1 introns. VS ribosyme has both cleavage and ligation activity and can perform both cleavage and ligation reactions efficiently in the absence of proteins. VS ribozyme undergo horizontal gene transfer with other Neuropora strains. VS ribozymes have nothing in common with other nucleolytic ribozymes.

VS RNA has a unique primary, secondary, and tertiary structure. The secondary structure of the VS ribozyme consists of six helical domains (Figure 1). Stem loop I forms the substrate domain while stem-loop II-VI forms the catalytic domain. When these 2 domains are synthesized in vitro separately, they can perform the self-cleavage reaction by trans-acting The substrate binds into a cleft which is made by two helices. The likely active site of the ribozyme is a very important nucleotide A756. The A730 loop and A756 nucleotide are critical to its function since they participate in the phosphoric transfer chemistry activity of the ribozyme

VS RNA is transcribed as a multimeric transcript from VS DNA. VS DNA contains a region coding reverse transcriptase necessary for replication of the VS RNA. Once transcribed VS RNA undergoes a site specific cleavage. VS RNA self-cleaves at a specific phosphodiester bond to produce a monomeric and few mutimeric transcripts. These transcripts then undergo a self-ligation and form a circular VS RNA. This circular VS RNA is the predominant form of VS found in Neurospora. VS ribozyme is a small catalytic motif embedded within this circular VS RNA. The majority of VS RNA is made up of 881 nucleotides

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