Involvement in human disease gives RNA elevated status

DNA, deoxyribonucleic acid, the material of genes, is doing very well. It is at the core of life, for in all cells it is DNA alone that replicates.

DNA is everywhere in the news, but what about its near-relation, RNA, ribonucleic acid? It is also crucial in cellular life - and a new and exciting role has just been revealed.

DNA carries the code for proteins. But in 1960, how the information from the DNA was used to make proteins was not known. It was thought that little particles containing RNA, ribosomes, carried the message from the DNA for making proteins. But there was evidence that this could not be true, as no new ribosomes were made when new proteins had to be made.

At a meeting at Cambridge University in 1960, molecular biologist Sydney Brenner has said "the penny dropped" when he and Francis Crick suddenly realised that there must be another RNA carrying the message.

Dr Brenner and molecular biologist Francois Jacob eventually discovered messenger RNA after adding magnesium to their experiments. Both have Nobel Prizes, but this should have been another one.

Messenger RNA carries the code for making proteins from the DNA to the ribosome. The messenger RNA is synthesised on the DNA gene for the protein, which acts as a template. It then leaves the DNA and binds to a ribosome and in a quite complex process, the code is then translated into the sequence of amino acids that make up a particular protein.

It is, of course, proteins that are the wizards of the cell, as they determine the form and function of the cell. For example, in muscle it is special proteins that enable the muscle to contract. Genes, by comparison, are rather boring and passive, but turning them on allows messenger RNA to be made, and thus the relevant proteins.

Enormous efforts are devoted to studying when and where genes are turned on during embryonic development, as well as in situations such as cancer where the wrong genes are turned on.

A peculiar feature of human DNA and related animals is that most - almost 98 per cent - of the DNA does not code for proteins, and so it has been a puzzle as to what it does.

Some of it is for controlling when and where a gene is turned on, as special proteins bind to these control regions and determine the on/off status of a gene. But the new view is that much of the DNA codes for special non-coding RNAs, which act as regulatory signals.

These non-coding RNAs can act by binding to messenger RNAs and effectively making them inactive, and they can also act as regulators of gene activity.

Much of the DNA is thus for these regulatory non-coding RNAs. As many as 20 per cent of all human genes can effectively be silenced by these non-coding RNAs.

There is also evidence that these RNAs are involved in human diseases ranging from cancer to schizophrenia.

RNA now has an elevated status. The level of complexity in the cell was known to be high before this discovery, but now goes even higher.

- INDEPENDENT