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A simple question that had occurred to me. Considering the small doubt of transcribed genes in both organelles, I would doubt it, but are there any known ribozymes strictly found in either mitochondria or chloroplasts?

UPDATE: Actually, I just thought of rRNA acting as a peptidyl transferase in mitochondrial ribosomes... Any other ideas?

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can't we consider ribosomes as colossal ribozymes ? – biogirl Apr 14 '14 at 18:12

You've already mentioned rRNA. An interesting review (Tanner, 2006), outlines some more:

  • Group I Introns - self-splicing; "They are abundant in fungal and plant mitochondria..."
  • Group II Introns - some have been shown to self-splice; "...they are found in fungal and plant mitochondria, in chloroplasts of plants ... and especially in the chloroplasts of the protist Euglena gracilis."
  • RNase P - involved in tRNA processing, found in mitochondria

None of these are strictly found in mitochondria or chloroplasts. However, the paper goes on to describe VS RNA ribozyme:

The mitochondria of certain strains of Neurospora contain the Varkud plasmid (a retroplasmid), which encodes a reverse transcriptase, and a small, unrelated, RNA (VS RNA). The VS RNA is transcribed from circular or multimeric VS plasmid DNA by a mitochondrial RNA polymerase, and the resulting transcripts are subsequently site-specifically cleaved and ligated to form circular, 881 nucleotides long, RNA monomers. These monomers are then reverse transcribed and made double stranded to form the mature VS plasmid.

In vitro transcribed VS RNA precursors are cleaved and ligated by the RNA itself and this is presumed to occur in vivo as well. Of all the self-cleaving RNAs, the catalytic properties of VS RNA are the most poorly understood.


Tanner NK. 2006. Ribozymes: the characteristics and properties of catalytic RNAs. FEMS Microbiol Rev. 23(3):257-275.

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