ena-STUDY-IZB-31-03-2015-17:10:58:996-152
Crammed, ambiguous genetic codes
In most nuclear genomes the genetic code appears frozen and largely unambiguous. For unknown reasons, among all eukaryotes, ciliates demonstrate a proclivity for reassigning the standard nuclear stop codons to amino acids, with seven variant genetic codes, including three new ones reported here. The key question is therefore: why is the nuclear genetic code so exceedingly stable in most eukaryotes, but not in ciliates? In ciliates, we have discovered the most sophisticated nuclear genetic codes, which paradoxically translate all 64 codons as standard amino acids, and recognize either one or all three stop codons. "Stop" codon depletion shortly before coding sequence ends suggests mRNA 3' ends are involved in stop/sense disambiguation. We propose that, together with stop codon depletion, ambiguity tolerance, including during stop codon readthrough, has enabled repeated genetic code diversification. Please note that the C. magnum genome assembly contains sequences both ciliate and resident bacterial sequences.
In most nuclear genomes the genetic code appears frozen and largely unambiguous. For unknown reasons, among all eukaryotes, ciliates demonstrate a proclivity for reassigning the standard nuclear stop codons to amino acids, with seven variant genetic codes, including three new ones reported here. The key question is therefore: why is the nuclear genetic code so exceedingly stable in most eukaryotes, but not in ciliates? In ciliates, we have discovered the most sophisticated nuclear genetic codes, which paradoxically translate all 64 codons as standard amino acids, and recognize either one or all three stop codons. "Stop" codon depletion shortly before coding sequence ends suggests mRNA 3' ends are involved in stop/sense disambiguation. We propose that, together with stop codon depletion, ambiguity tolerance, including during stop codon readthrough, has enabled repeated genetic code diversification. Please note that the C. magnum genome assembly contains sequences both ciliate and resident bacterial sequences.