The Hindu : Three letters that could save lives

Online edition of India's National Newspaper
Sunday, Apr 13, 2003

International

International

Three letters that could save lives

London APRIL 12. Scientists have found a new and highly precise way to toss a spanner into the works of a cell. Much remains to be understood about this powerful way to shut down, or "silence'', genes but it seems to play a central role in the development of plants and animals, as well as in fending off illnesses.

Now, they are beginning to exploit this knowledge. Some are using it to investigate what genes do, while others hope to create new treatments for diseases such as cancer. Recently, the technique passed its first test to show it could be used to combat AIDS, hepatitis and other illnesses. Silence is indeed golden.

The advance rests on new insights into genetic code called ribonucleic acid (RNA), long thought to be the dowdy ancestor of its glamorous cousin deoxyribonucleic acid (DNA).

While most are unsure what RNA is, DNA is a household word. Indeed, events across the planet this month will mark the 50th anniversary of the discovery, in Cambridge, that DNA is formed from two molecular strands wound into a double helix.

Like DNA, RNA consists of strings of chemicals — "letters'' — that spell out the genetic code. The letters are represented by A, C, G and either T in DNA or U in RNA. C always binds to G. A binds only to T or U. A single-strand of DNA or RNA can bind to another strand consisting of complementary letters.

Until recently, it was thought that RNA carried out DNA's commands, in effect deciding what genetic information to turn into action. Then, the DNA's double helix unwinds and its genetic code is copied on to a single-stranded "messenger'' RNA. In turn, the messenger RNA shuttles the code from the heart of cells to ribosomes, the "factories'' that make the proteins that build and operate cells.

So why bother, then, to study the RNA middleman when DNA holds the recipe of life? The reason is that RNA has found a new starring role in the cell.

The first hint of this came six years ago, when Andrew Fire of the Carnegie Institution, Washington, Craig Mello of the University of Massachusetts and colleagues found that double-stranded RNA can be used to shut down specific genes. Their discovery, called RNA interference, or RNAi, was published in the journal Nature and is now widely used as a research tool.

Another clue was from David Baulcombe and Andrew Hamilton in the Sainsbury Laboratory, Norwich, England. They discovered RNA fragments called short interfering RNAs, or siRNAs, are used by cells to fight viruses. Their work complemented the animal studies of Fire and Mello because siRNAs are fragments of double-stranded RNA.

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