Transfer RNA: Its Role in Decoding the Message

Abstract

In replication and transcription, genetic information is transferred from one nucleic acid molecule to another, to an identical molecule or to a molecular species at least very similar in its chemical structure. Information transfer in these steps is basically a copying process. At the stage of translation a more complex form of information transfer is taking place: not only is the chemical structure of the mRNA which is carrying the message basically different from that of the protein molecule in which the genetic information is eventually expressed, but also in the former, the message is encoded in a triplet code which has to be translated into the sequence of single amino acids. Instead of a copying mechanism, a decoding mechanism is at work, and this requires specific adaptor molecules which can recognise and interact with both the trinucleotide codons and the corresponding amino acids. Early studies on the mechanism of protein synthesis had already recognised that the adaptor molecules fulfilling this function were the transfer RNAs (tRNAs). These small RNA molecules have specific sites for interaction with nucleotide triplets and also sites for binding amino acids. They specifically select amino acids which they can carry to the site of protein synthesis where, in the presence of the appropriate codon, they can bind to the ribosome and thus direct the amino acid into the right position in the polypeptide chain. This function is carried out in a series of consecutive steps, involving interactions with a number of specific proteins and also with other RNAs. These specific interactions ensure that translation of the genetic message occurs with very high accuracy: the frequency of errors in translation is less than 1 to 3000 per codon¹.