Discovery of a fundamental limit to the evolution of the genetic code
A study performed at IRB Barcelona offers an explanation as to why the genetic code stopped growing 3,000 million years ago. This is attributed to the structure of transfer RNAs—the key molecules in the translation of genes into proteins. The genetic code is limited to 20 amino acids—the building blocks of proteins—the maximum number that prevents systematic mutations, which are fatal for life. The discovery could have applications in synthetic biology.
|3D respresentation of a transfer RNA (tRNA). These molecules are crucial for the translation of genes |
into proteins and they are also the reason why the genetic code cannot exceed 20 amino acid
[Credit: Pablo Dans, IRB Barcelona]
Headed by ICREA researcher Lluis Ribas de Pouplana at the Institute for Research in Biomedicine (IRB Barcelona) and in collaboration with Fyodor A. Kondrashov, at the Centre for Genomic Regulation (CRG) and Modesto Orozco, from IRB Barcelona, the team of scientists has demonstrated that the genetic code evolved to include a maximum of 20 amino acids and that it was unable to grow further because of a functional limitation of transfer RNAs—the molecules that serve as interpreters between the language of genes and that of proteins. This halt in the increase in the complexity of life happened more than 3,000 million years ago, before the separate evolution of bacteria, eukaryotes and archaebacteria, as all organisms use the same code to produce proteins from genetic information.
A limitation imposed by shape
Saturation of the genetic code has its origin in transfer RNAs (tRNAs), the molecules responsible for recognising genetic information and carrying the corresponding amino acid to the ribosome, the place where chain of amino acids are made into proteins following the information encoded in a given gene. However, the cavity of the ribosome into which the tRNAs have to fit means that these molecules have to adopt an L-shape, and there is very little possibility of variation between them.
|Genetic code. Every three letters of genetic information (triplets or codons) correspond |
to one of the amino acids or to a “stop signal” that marks the end of the protein.
Eg., the codon GCT represents the amino acid alanine [Credit: yourgenome.org]
Application in synthetic biology
One of the goals of synthetic biology is to increase the genetic code and to modify it to build proteins with different amino acids in order to achieve novel functions. For this purpose, researchers use organisms such as bacteria in highly controlled conditions to make proteins of given characteristics. "But this is really difficult to do and our work demonstrates that the conflict of identify between synthetic tRNAs designed in the lab and existing tRNAs has to be avoided if we are to achieve more effective biotechnological systems," concludes the researcher.
Source: Institute for Research in Biomedicine (IRB Barcelona) [May 02, 2016]