Codon reading patterns in Saccharomyces cerevisiae mitochondria based on sequences of mitochondrial tRNAs

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Abstract
The sequences of Saccharomyces cerevisiae mitochondrial tRNA1 Arg, tRNA2 Arg, tRNAGly, tRNA2 Lys tRNALeu and tRNAPro are reported. Special structural features were found in tRNAPro, which has A8, C21, A48 instead of the constant residues U8, A21 and pyrimidine 48, and in tRNA2 Lys, which has a U excluded from basepairing and bulging out from the TΨC stem. The tRNA1 Arg, tRNA2 Lys and tRNALeu, which belong to two-codon families ending in a purine, have a modified uridine in the wobble position, which prevents misreading of C and U. It is likely to be 5-carboxymethylaminomethyluridine. tRNAGly and tRNAPro have an unmodified uridine in the wobble position allowing the reading of all four codons of a four-codon family. However, tRNA2 Arg, which is a minor species and belongs to the CGN four-codon family, has an unmodified A in the wobble position. This very unusual feature raises the problem of the mechanism by which the codons CGA, CGG and CGC are recognized.