High molecular mass amino acyl-tRNA synthetase complexes in eukaryotes

Abstract

Aminoacyl-t RNA synthetases (AARS) are enzymes which play an indispensable role in protein biosynthe- sis by catalyzing the formation of aminoacyl-tRNA from amino acid, the cognate tRNA, and ATP by highly selective intermolecular interactions [57]. Joachimiak and Barciszewski [41] have provided an extensive compilation of the properties of the amino- acyl-tRNA synthetases; however, information on the eukaryotic highM r (HMr) complexes of aminoacyl-tRNA synthetases was lacking. Here, we intend to fill this void by providing a summary of the properties of the eukaryotic aminoacyl-tRNA synthetase complexes. Eukaryotic aminoacyl-tRNA synthetases may occur as complexes with Mr-values of >106 in contrast to the prokaryotic counterparts which have Mr-values of <250 000. These eukaryotic HMr--AARS complexes appear ubiquitous in a wide spectrum of cell types from yeast to human placenta as shown in table 1. Although not all 20 aminoacyl-tRNA synthetases were examined in each case shown in table 1, it appears that the AARS commonly associated with M r complexes are those specific for Arg, Gin, Glu, fie, Leu, Lys and Met. The properties of these HMr-AARS complexes are most consistent with multienzyme complexes of aminoacyl-tRNA synthetases [ 19,20,43, 46]. The physicochemical properties, composition, and stoichiometry of the more rigorously character- ized complexes are shown in table 2. The mechanism(s) of intermolecular interaction between the aminoacyl-tRNA synthetases is not known, but the putative interactions of aminoacyl- tRNA synthetases with a variety of biomolecules have been suggested to play a role in complex formation as shown in table 3. Our present knowledge of the func- * To whom correspondences should be addressed tional significance of HMr--AARS is profoundly lack- ing; however, interactions of the aminoacyl-tRNA synthetases with other components of the protein biosynthetic machinery and other enzymes suggest the intriguing possibility of higher organization of eukaryotic protein biosynthesis. Table 4 is a summary of the possible interactions of the aminoacyl-tRNA synthetases with subcellular components and other enzymes. This presentation is a brief summary of the prop- erties of the high molecular weight eukaryotic amino- acyl-tRNA synthetase complexes. We hope that this compilation will complement that presented in [41 ] and will provide useful information for workers in this and other related fields.