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

Abstract

The sequences of Saccharomyces cerevisiae mitochondrial tRNA₁ ^Arg, tRNA₂ ^Arg, tRNA^Gly, tRNA₂ ^Lys tRNA^Leu and tRNA^Pro are reported. Special structural features were found in tRNA^Pro, 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 tRNA^Leu, 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. tRNA^Gly and tRNA^Pro 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.