Heriot-Watt Mathematics Report Series
HWM00-16, 17 Jul 2000
Evolution of RNA editing in trypanosome mitochondria
L Simpson, O H Thiemann, N J Savill, J D Alfonzo and D A Maslov
Abstract
Two different RNA editing systems have been described in the kinetoplast-mitochondrion of trypanosomatid protists, The first involves the
precise insertion and deletion of U residues mostly within the coding regions of maxicircle-encoded mRNAs to produce open reading frames.
This editing is mediated by short overlapping complementary guide RNAs encoded in both the maxicircle and the minicircle molecules and
involves a series of enzymatic cleavage-ligation steps. The second editing system is a C-34 to U-34 modification in the anticodon of the
imported tRNA(Trp), thereby permitting the decoding of the UGA stop codon as tryptophan, U-insertion editing probably originated in an
ancestor of the kinetoplastid lineage and appears to have evolved in some cases by the replacement of the original pan-edited cryptogene
with a partially edited cDNA, The driving force for the evolutionary fixation of these retroposition events was postulated to be the stochastic
loss of entire minicircle sequence classes and their encoded guide RNAs upon segregation of the single kinetoplast DNA network into
daughter cells at cell division. A large plasticity in the relative abundance of minicircle sequence classes has been observed during cell
culture in the laboratory. Computer simulations provide theoretical evidence for this plasticity if a random distribution and segregation model of
minicircles is assumed. The possible evolutionary relationship of the C to U and U-insertion editing systems is discussed.
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Publication
L Simpson, O H Thiemann, J D Alfonzo, NJ Savill
, Evolution of RNA editing in trypanosome mitochondria, Proceedings of the National Academy of Sciences of the USA, 97, 6986-6993, (2000).
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