Scrambled ribosomal RNA gene pieces in chlamydomonas reinhardtii mitochondrial DNA

Extrachromosomal DNA in the Apicomplexa

“…Such an arrangement in a mitochondrial genome has been found only once before, in the alga Chlamydomonas reinhardtii (8,46), but in this case all the fragments were encoded on the same DNA strand. Disrupted genes for cytoplasmic rRNAs also occur in Crithidia, Trypanosoma, and Euglena spp.…”

Evidence that the fragmented ribosomal RNAs of Chlamydomonas mitochondria are associated with ribosomes

“…As a result, we cannot distinguish between the hypotheses that mitochondrial ribosome biogenesis in Chlamydomonas proceeds either by the association of small RNP particles composed of individual mitochondrial rRNAs and ribosomal-proteins [5] or that a transcript(s) containing interspersed rRNA domains form(s) the ribosomal subunit cores through base-pairing in larger RNP particles that are later processed to generate the mature mitochondrial rRNA termini.…”

“…Boer and Gray [5], in considering whether the various LSU and SSU rRNA gene pieces identified in Chlamydomonas mtDNA are functional, suggested that rigorous proof for such a conclusion would require a demonstration that the RNAs transcribed from these coding regions are indeed present in subunits of Chlamydomonas mitochondrial ribosomes and that such ribosomes are active in mitochondrial protein synthesis. Based on the results presented here, we propose that the first of these steps has been accomplished.…”

“…The observation that these rRNA subfragments have the potential to form standard rRNA secondary structures through inter-molecular base pairing suggests that they could function in the Chlamydomonas mitochondrial ribosomes as a non-covalent network of small RNAs. In the case of C. reinhardtii, moreover, the mitochondrial rRNAs are more abundant than the protein-coding transcripts, as would be predicted for functional rRNA molecules [5]. Finally, the fact that…”

“…Small subunit (SSU) and large subunit (LSU) rRNAs are encoded in the mtDNAs of C. reinhardtii and Chlarnydomonas eugametos. The coding regions for these rRNAs, however, are distributed into separate gene pieces which are scrambled in order and are interspersed with each other and with protein-coding and tRNA genes [5][6][7]. This unusual gene organization raises the question as to whether these small transcripts function in mitochondrial ribosomes.…”