Hidden Treasures of the Genetic Systems in Yeast Mitochondria

Mitochondria are the masters of evolutionary tinkering, which can be exemplified by both the remarkable variability of the mitochondrial genome architectures and numerous noncanonical features involved in the mitochondrial gene expression. Evolutionary experimentation in these living test tubes is facilitated by their polyploid nature and resulted in a number of surprising oddities identified in various eukaryotic lineages. Excellent examples of these peculiarities are provided by mitochondrial genetic systems of unicellular fungi classified as the budding yeasts. Perhaps the most perplexing eccentricity found in yeast mitochondria are the bypassing elements (byps) residing in the reading frames of protein-coding genes. Ribosomes ignore byps during translation by means of programmed translational bypassing. Massive occurrence of these coding gaps in certain yeast species raises the questions on their evolutionary origin and mobility as well as the molecular mechanism of translational bypassing.