Each human has 100 billion km of total DNA, enough to reach sun and come back 300 times. But of the 3.3 billion nucleotides of human genome, less than two per cent code for proteins while the remaining 98 per cent is non-coding in nature and generally described as “junk DNA”.

But scientists from the Centre for Cellular and Molecular Biology (CCMB) here have found that all that non-coding part is not junk. While more than 50 per cent of the non-coding DNA was repetitive, simple sequence repeats (SSRs) account for about three per cent of the human genome.

In the study conducted by chief scientist, Rakesh K. Mishra and his group, it was found that one of the SSRs, the GATA repeat had significant regulatory role in gene expression by functioning as a boundary, separating functional domains of genome. The results of the study were published in May 14 issue of ‘Nature Communications’.

Addressing a press conference here on Wednesday, CCMB Director, Dr. Ch. Mohan Rao, described it as a “very important finding”. He said that while the size of genome was found to increase from simple to complex organisms, the number of protein coding genes do not increase appreciably.

The accumulation of non-coding part of the genome (whose function remains largely to be established) appears to be the driving force behind the evolution of complexity in living organisms. This indicates that the biological complexity had not evolved by the addition of more genes to the genome but by more sophisticated regulation of the pre-existing genes. Dr. Rakesh Mishra pointed out that SSRs, including GATA repeats were known to show polymorphisms-small size variations in size of the repeat at different loci in the genome within a population. Such variations were the basis of DNA finger printing that could establish the genetic identity of a person.

In the study, the scientists have inserted human DNA’s SSR into Drosophila to assay its functions.