engleski

MITOCHONDRIAL AND CYTOPLASMIC SERYL-tRNA SYNTHETASES FROM Zea mays

In order to analyze the structure/function relationships among cytoplasmic and organellar seryl-tRNA synthetases (SerRS), we have characterized two Zea mays cDNAs. One encodes a protein (SerZMc) with significant similarity to other eukaryotic cytoplasmic SerRS enzymes, while the translation product of the other gene (SerZMm) is more similar to prokaryotic SerRSs. Phylogenetic analyses have revealed that mitochondrial seryl-tRNA synthetases are evolutionary distant from the cytosolic enzymes. The two known mitochondrial SerRS sequences, from yeast (SerSCm) and maize (SerZMm), form a marginally significant clade, apparently due to increased mutation rate observed in most proteins with mitochondrial function. To demonstrate the functional identity of SerZMm, the gene sequence encoding the putative mature protein was used for in vivo complementation of a temperature-sensitive Escherichia coli serS mutant. Additionally, Saccharomyces cerevisiae respiratory defficient strain, obtained by SerSCm gene disruption, was tested for complementation with a gene fusion, consisting of the proposed yeast SerSCm mitochondrial targeting signal and mature SerZMm. The mature SerZMm protein overexpressed in E. coli efficiently aminoacylated bacterial tRNASer, while yeast tRNA was a poor substrate. Current studies are aimed at defining the differences in substrate specificities between cytoplasmic and organellar seryl-tRNA synthetases.

aminoacyl-tRNA synthetases; tRNA

nije evidentirano