Archaeal aminoacyl-tRNA synthesis: Diversity replaces dogma

Accurate aminoacyl-tRNA synthesis is essential for faithful translation of the genetic code and consequently has been intensively studied for over thr ee decades. Until recently, the study of aminoacyl-tRNA synthesis in archae a had received little attention. However, as in so many areas of molecular biology, the advent of archaeal genome sequencing has no-cv drawn researche rs to this field. Investigations with archaea have already led to the disco very of novel pathways and enzymes for the synthesis of numerous aminoacyl- tRNAs. The most surprising of these findings has been a transamidation path way for the synthesis of asparaginyl-tRNA and a novel lysyl-tRNA synthetase . In addition, seryl- and phenylalanyl-tRNA synthetases that are only margi nally related to known examples outside the archaea have been characterized , and the mechanism of cysteinyl-tRNA formation in Methanococcus jannnschii and Methanobacterium thermoautotrophicum is still unknown. These results h ave revealed completely unexpected levels of complexity and diversity, ques tioning the notion that aminoacyl-tRNA synthesis is one of the most conserv ed functions in gene expression. It has now become clear that the distribut ion of the various mechanisms of aminoacyl-tRNA synthesis in extant organis ms has been determined by numerous gene transfer events, indicating that, w hile the process of protein biosynthesis is orthologous, its constituents a re not.