Two new letters in the DNA alphabet
The alphabet of DNA – four nucleotide bases – is supplemented with two more letters. They can only be used for marginal notes: artificial nucleotides are not suitable for transmitting information about the amino acids that make up proteins, but they are easily copied by polymerase enzymes when chromosomes are doubled.
A group of scientists led by Floyd Romesberg from the Ellen Scripps Institute (La Jolla, California, USA) spent almost ten years creating these nucleotides. The researchers created a library of about 200 bases, similar in structure to the molecules known to all adenine, thymine, guanine and cytosine. Unfortunately, none of these molecules were sufficiently similar to natural bases, and DNA polymerases could not copy DNA strands including these nucleotides.
As it often happens, scientists were helped by perseverance and a lucky chance. A random search of about 3,600 more specially synthesized nucleotide bases led to the discovery of a suitable pair. The new letters have not yet received personal names, and they are still called the conditional codes dSICS and dMMO2. We should suggest designating them with the letters R – Romsberg and L, in honor of his graduate student Aaron Leconte (article by Aaron M. Leconte et al. Discovery, Characterization, and Optimization of an Unnatural Base Pair for Expansion of the Genetic Alphabet published on 25.01.2008 in J.Am.Chem.Soc.)
After the first breakthrough, the second stage of routine work began: dSICS nucleotides were more easily paired with each other than with dMMO2. I had to go through about 15 dSICS modifications, and the option with the d5SICS code turned out to be exactly what I needed. Now, having understood some patterns, the researchers plan to continue studying the mechanisms of recognition of nucleotides by polymerases and continue the search for new artificial letters of the genetic code.
Artificial bases, although they are not able to encode amino acids, can be used as markers in the chromosomes of genetically modified organisms. They can be used both in theoretical research – for example, in the study of the mechanisms of transcription and translation (translation of information along the DNA-RNA-protein chain), and in applied, including in nanotechnology, in which DNA is often used due to the ability of nucleotides to complement each other.
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of NewScientist
31.01.2008