Scientists have discovered a giant DNA — the length of millions of nucleotides (basic "building blocks" of DNA) — the structures that are singled out from the surrounding genetic "background" by the typical content of certain "letters". The researchers' work is published in the journal Physical Review E, and wrote about it briefly portal Physical Review Focus.
DNA strands containing the genetic information of an organism and consists of four types of nucleotides (which represent the letters A, T, G and C). Certain combinations of nucleotides encoding a different amino acid — basic components of proteins, and coding regions separate proteins called genes (also referred to as regions of DNA genes encoding the proteins are not as specific RNA). Also there are in the genome intergenic regions, the function of which is still not clear.
In addition to the functional separation (genes and intergenic regions) of DNA can be broken down into fragments that differ in nucleotide composition. For example, some areas are characterized by a larger than average number of pairs following each other nucleotides C and D (such pairs are called CpG — from the Latin names of these nucleotides). DNA analysis showed that the genome clearly distinguished isochor — sites with a certain percentage of CpG-pairs that differ from the average in the human genome. Isochores length is usually several hundred thousand nucleotides.
The authors have found a new job even larger — up to tens of millions of nucleotides — the structures, which are also characterized by a certain degree of CpG-pairs. That is, each chromosome consists of several such superstructures, in which about two hundred genes.
Scientists have conducted a preliminary analysis of the genes that make them discovered the structure. For this, they have characterized the genes in several structures, attributing them to certain categories — genes encoding membrane proteins, genes involved in cell signaling, the genes involved in the coordination of metabolism and so on (each gene can belong to multiple categories). On average, two genes randomly selected from the genome coincide six categories. Two genes taken from a isochors coincide approximately 15 categories. The two genes belonging to the same superstructure, common proved about 18 categories.
While scientists can not say what is the biological significance of found their superstructures. This is not the first large formations found in the genome — for example, in the genomic DNA previously been found enormous loop containing genes that currently operate in the same mode (e.g., which is an active protein synthesis). The science that studies these "nadgenomnye" structure, called epigenetics.