Final answer:
Pre-transfer proofreading by AARSs is a quality control mechanism that prevents the inclusion of incorrect amino acids into proteins by hydrolyzing incorrect aminoacyl-adenylate (AA~AMP). This process maintains the fidelity of protein synthesis and is an evolutionarily conserved function in some AARSs.
Step-by-step explanation:
The pre-transfer proofreading of aminoacyl-tRNA synthetases (AARSs) is a crucial quality control step that ensures the accuracy of protein synthesis. During this process, AARSs hydrolyze incorrectly paired aminoacyl-adenylate (AA~AMP), which prevents the attachment of non-cognate amino acids to tRNAs. This function is essential for maintaining cellular homeostasis and is found in ten out of the twenty existing AARSs. The editing function is phylogenetically conserved in some AARSs and varies among different species.
Pre-transfer proofreading by AARSs protects the integrity of the genetic code by preferentially binding and subsequently hydrolyzing incorrect AA~AMPs at their catalytic domains before these amino acids are transferred to tRNA. As a result, only the correct amino acids are bonded to their cognate tRNAs, preventing errors in protein synthesis that could be deleterious to the cell. The evolution of these editing mechanisms links back to the ancestral AARSs that were involved in non-coded peptide synthesis in the ancient Thioester World.