The Varkud satellite ribozyme is an RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that carries out the cleavage of a phosphodiester bond.

Structure

The VS ribozyme

Ribozyme

A ribozyme is an RNA molecule with a well defined tertiary structure that enables it to catalyze a chemical reaction. Ribozyme means ribonucleic acid enzyme. It may also be called an RNA enzyme or catalytic RNA. Many natural ribozymes catalyze either the hydrolysis of one of their own...

 is composed of 5 helices that form an H shape (helices II to VI). The first helix (I) contains the substrate cleavage site in the stem-loop

Stem-loop

Stem-loop intramolecular base pairing is a pattern that can occur in single-stranded DNA or, more commonly, in RNA. The structure is also known as a hairpin or hairpin loop. It occurs when two regions of the same strand, usually complementary in nucleotide sequence when read in opposite directions,...

.

The activity of the VS ribozyme is thought to require a long range pseudoknot

Long range pseudoknots

A long range pseudoknot is a pseudoknot containing a long loop region, and may be a mechanism of translational control.A long range pseudoknot is thought to negatively regulate the translation of the IF3-L35-L20 operon in E. coli. This operon encodes the translation factor 3 and ribosomal proteins...

 structure.

Species distribution

The VS ribozyme has only been found in mitochondrial DNA of Neurospora

Neurospora

Neurospora is a genus of Ascomycete fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons....

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