Previous studies showed that VAS1 of Saccharomyces cerevisiae encodes both cytosolic and mitochondrial forms of valyl-tRNA synthetase (ValRS) through alternative initiation of translation. We show herein that except for Schizosaccharomyces pombe, all yeast species studied contained a single ValRS gene encoding both forms, and all of the mature protein forms deduced from those genes possessed an N-terminal appended domain which was absent from their bacterial relatives. In contrast, S. pombe contained two distinct nuclear ValRS genes, one encoding the mitochondrial form and the other its cytosolic counterpart. While the cytosolic form closely resembles other yeast ValRS sequences ( approximately 60% identity), the mitochondrial form exhibits significant divergence from others ( approximately 35% identity). Both genes are active and essential for the survival of the yeast. Most conspicuously, the mitochondrial form lacks the characteristic appended domain. A phylogenetic analysis further suggested that both forms of S. pombe ValRS are of mitochondrial origin, and the mitochondrial form is ancestral to the cytoplasmic form.
Date:
2010-06
Relation:
Molecular Biology and Evolution. 2010 Jun;27(6):1415-1424.
