ABSTRACT
Transfer ribonucleic acid (tRNA) interacts with many different molecules in the cell. During the translation process tRNA interacts with aminoacyl-tRNA ligases, initiation factors, elongation factor Tu, elongation factor G, messenger ribonucleic acid, ribosomes, and peptidylhydrolase. The presence of so many different modified nucleosides in the tRNA introduces local chemical microenvironments in the molecule that may be recognition sites for proteins or nucleic acids and may change the conformation of the tRNA. Transfer RNA from all organisms contains modified nucleosides, which are derivatives of the four normal nucleosides: adenosine, guanosine, uridine and cytidine. Transfer RNA modifying enzymes are highly specific. A mutation in a structural gene for one tRNA modifying enzyme seems only to influence the formation of the corresponding modified nucleoside; for instance, the deficiency caused by a genetically defective tRNA modifying enzyme does not prevent other modification reactions from occurring.
