engleski

Functional and evolutionary analysis of organellar seryl-tRNA synthetases

Seryl-tRNA synthetases are essential enzymes that catalyse the formation of ester bond between serine and tRNASer. Organellar seryl tRNA synthetases are coded by a separate set of genes in all organisms studied so far. Thus it is assumed that they have evolved independently from the genes for cytoplasmic enzymes. We have recently PCR- amplified the gene for mitochondrial seryl-tRNA synthetase from yeast Saccharomyces cerevisiae. The gene for organellar seryl-tRNA synthetase from maize has also been cloned, sequenced and the enzyme shown to recognize Escherichia coli tRNASer in vivo and in vitro. Both organellar enzymes possess N-terminal extensions which are identified as signal sequences for translocation across the organellar membranes. Our phylogenetic analyses demonstrate that these two enzymes share the greatest structural similarity among the known primary structures of seryl-tRNA synthetases from different organisms. Organellar enzymes are considerably divergent with respect to all cytosolic enzymes, in accordance with the endosymbiotic theory. These evolutionary data were reconfirmed by various phylogenetic methods. The organellar seryl-tRNA synthetases from maize and yeast are consistently grouped together in a clade, verifying our data as statistically highly significant. The homology based models of the two enzymes have been constructed, and the distance matrix obtained by comparison with other models of seryl-tRNA synthetases also strongly supports the notion of the greatest evolutionary similarity between those organellar enzymes.

aminoacyl-tRNA synthetases ; evolution

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