‘Copy-and-paste DNA’ more common than previously believed

WASHINGTON - Movable sequences of DNA-also known as ‘Copy-and-paste DNA’-which give rise to genetic variability and sometimes cause specific diseases, are far more common than previously thought, according to researchers at the University of Leicester.

For the study, Dr Richard Badge and his collaborators examined L1 (or LINE-1) retrotransposons- DNA sequences which can ‘copy and paste’ their genetic code around the genome.

By breaking up genes, L1s can be responsible for some rare instances of genetic disease.

The researchers developed an innovative technique to find L1s, using short sequences of DNA called fosmids.

These are free-floating loops of DNA, which can be easily transported into bacterial cells, and can carry pieces of human DNA.

Each fosmid can hold only a specific amount of DNA, approximately 40,000 bases.

Thus, by comparing the two ends of a piece of human DNA held in a fosmid, against their known positions in the human genome sequence, the scientists could quickly and easily spot differences in size.

“We’re just looking at each end of the sequence and seeing if they’re the right distance apart. This shows us the existence of insertions (which we’re interested in) and also deletions. This technology is completely unbiased - it doesn’t care what the insertion/deletion actually is, just whether it’s there,” said Badge.

After identifying the insertions, the researchers wanted to see if they could ‘jump’ in cultured human cells and how common they are.

“Previous studies suggested that lots of L1s should jump - but don’t. But about half of the L1s we found jump really well, which was very surprising. We found about 65 elements, which had not been previously identified,” said Badge.

“This tells us that active human retrotransposons are much more common than we expected. Individual active L1 retrotransposons are quite rare - but there are a lot of them,” he added.

The study is published in the latest issue of Cell. (ANI)