ABSTRACT
Transfer RNA (tRNA) molecules play an important role in protein synthesis. Each tRNA becomes covalently bonded to a specific amino acid to form aminoacyl-tRNA which recognizes the corresponding codon in mRNA and ensures that the correct amino acid is added to the growing polypeptide chain. The rRNA transcription units in E. coli contain some tRNA genes that are transcribed and processed at the time of rRNA transcription. In eukaryotes, the tRNA genes exist as multiple copies and are transcribed by RNA polymerase III (RNA Pol III). As in prokaryotes, several tRNAs may be transcribed together to yield a single pre-tRNA molecule that is then processed to release the mature tRNAs. The promoters of eukaryotic tRNA genes are unusual in that the transcriptional control elements are located downstream of the transcriptional start site. Transfer RNA molecules are notable for containing unusual nucleotides such as 1-methylguanosine (m1G), pseudouridine (ψ),dihydrouridine (D), inosine (I) and 4-thiouridine (S4U).
