The evolution of aminoacyl-tRNA synthetases in chromerids

Aminoacyl-tRNA synthetases (aaRS) are enzymes that catalyze the ligation of tRNAs to their cognate amino acids. There are aaRSs specific to each of the 20 standard amino acids. These enzymes are divided into two classes, class I and class II, which are unrelated in both sequence and structure. aaRSs can function in multiple sub-cellular compartments due to the phenomenon of dual targeting. We searched the total predicted proteins of Chromera velia and Vitrella brassicaformis for aaRSs proteins. Phylogenetic analyses of all available 21 aaRSs sequences were performed using maximum likelihood and Bayesian inference. Computer predictions of the intracellular location of the identified enzymes were performed to test the multiple targeting hypothesis. Fifty genes encoding aaRS were identified in C. velia, while only 38 aaRSs were found in V. brassicaformis. Forty-five percent of C. velia’s aaRss are encoded by three distinct loci, whereas 35% of aaRSs are encoded by two distinct loci. Interestingly, both tryRS and trpRS are encoded by only one locus and valRS is encoded by five loci. In contrast, 70% of the V. brassicaformis aaRSs are encoded by just two distinct loci. Most of the molecular phylogenies of aaRSs indicate that for each aaRS the evolutionary pattern is different and eukaryotic genes are usually retained. Targeting predictions show that particular enzymes are not often used in the compartments where they originate.