Unilateral flexibility in tRNASer recognition by heterologous seryl-tRNA synthetases

Background: Aminoacyl-tRNA synthetases (aaRSs) are ancient proteins that establish the rules of the genetic code through aminoacylation reactions, where a specific amino acid is joined to its cognate tRNA. It is believed that aaRSs and tRNA isoacceptors specific for a particular amino acid have coevolved and, as a consequence, heterologous recognition across taxonomic domains is often prevented. Materials and Methods: tRNAs were generated by in vitro transcription of corresponding synthetic genes, while the synthetases were isolated from bacterial or yeast overproducing strains. The macromolecular interactions were studied by aminoacylation and gel-shift electrophoresis, under equilibrium or non-equilibrium conditions. Results: In serine aminoacylation system it seems that the enzymes from different organisms are much more diverse than cogitate tRNAs(Ser), which usually comprise rather conserved major recognition elements. In the present study we explored heterologous serylation among macromolecular partners from various organisms or cellular compartments. Different seryl-tRNA synthetases (SerRS) showed variable degree of flexibility in cross-domain charging, which is often unilateral. Conclusion: The most stringent is the recognition of cognate tRNA by Escherichia coli SerRS, somewhat more flexible is the counterpart from Saccharomyces cerevisiae, followed by SerRS from methanogenic archaea Methanococcus jannaschii and Methanococcus maripaludis, which serylate tRNA(Ser) from all three domains of life. Interestingly, methanogenic SerRS from? the third archaeon Methanopyrus kandleri discriminates yeast tRNA(Ser). Maize organellar SerRS aminoacylates tRNA(Ser) of bacterial origin.