Monday, 25 May 2009

Junk DNA that's not a junk at all, says CCMB

Syed Akbar
Hyderabad: In a major scientific breakthrough the city-based Centre for Cellular and Molecular Biology has found that the so-called "Junk DNA" present on the human Y-chromosome is not at all "junk" but contains properties that could control cell division in testes.
The study, first of its kind in the world, gives an insight on male sterility factors and might give vital information on what prevents cancer of testes in a majority of male populations.
"This is the first demonstration that junk DNA interacts and controls the function of a gene located on another chromosome, which is not limited to a sex. This study opens up a new approach to unravel the function of the non-coding DNA in our genome. New discoveries of RNA world and its role in gene expression are considered to be a great revolution in modern biology, which is over-shadowing the importance of DNA. It is suggested that protein-coding genes may not be the movers and shakers of human evolution, as scientists once thought. Perhaps we should stop looking at proteins and start looking at non-coding DNA," CCMB director Dr Lalji Singh said.
More than 98.8 per cent of human genome is made up of non-coding DNA generally referred to as "junk". Less than 1.2 per cent of human DNA codes for protein. One of the biggest challenges in the field of modern biology is to find out the function of junk DNA. The Y chromosome is of interest to man because it carries genes for maleness.
This chromosome contains DNA specifically present in male. Two-thirds of Y chromosome is made up of repetitive DNA, which has been thought of as junk. The present study at CCMB presents unequivocal evidence that 40 mega base repeat block of the Y-chromosome, which was earlier perceived as junk DNA, is transcribed into RNA but not translated into protein as it does not have the required features to be translated.
However, the CCMB study clearly demonstrates that the Y-chromosomal junk DNA is transcribed into two novel RNAs in a developmental-state-specific and testis-specific manner, one of which controls the expression of a protein by a mechanism described as trans-splicing wherein RNAs from different chromosomes/genes recombine to produce chemeric RNAs, Dr Singh observed.
The results of the study released to media on Friday has been published in Genome Research.

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