engleski

MAIZE SERYL-tRNA SYNTHETASES FROM DIFFERENT CELLULAR COMPARTMENTS

In higher plants protein synthesis takes place in the cytosol, mitochondria and chloroplasts. Each compartment relies on its own set of aminoayl-tRNA synthetases, that are encoded in the nucleus, synthesized in the cytosol, and imported into the organell. In order to analyze the structure/function relationships among plant cytosolic and organellar seryl-tRNA synthetases (SerRS), we have caracterized two Zea mays cDNAs. One cDNA clone encodes a protein (SerZMc) with significant similarity to eukaryotic cytosolic SerRS enzymes, especially to Arabidopsis thaliana SerRS. These two plant cytosolic enzymes share over 50 % identity. Besides, SerZMc has highly basic C-terminal extension characterizing all eukaryotic cytosolic SerRS enzymes. The other cDNA clone carries a gene for a protein (SerZMm) that probably functions in maize mitochondria. It is more similar to eubacterial SerRSs what is in accordance with the endosymbiotic theory on origin of organelles. To demonstrate the functional identity of SerZMm, the region of the gene encoding the putative mature protein was used for in vivo complementation of a temperature-sensitive Escherichia coli serS mutant. The mature SerZMm protein overexpressed in E. coli efficiently aminoacylated bacterial tRNASer, while yeast tRNA was a poor substrate. SerZMm N-terminal sequence shows distinctive features of mitochondrial targeting signals. Mitochondrial location of SerZMm is also suggested from phylogenetic analysis of a number of SerRS enzymes that reveals significant clustering of SerZMm and putative mitochondrial yeast SerRS.

seryl-tRNA synthetases; maize; organellar

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