In a classic case of under dog becoming top dog, the RNA has displaced the DNA as the happening chemical. From being a mere carrier of information from the DNA in the center of the cell to the many parts where proteins are made, RNA is slowly emerging to be the regulator with power to turn off whole chromosomes! Not just that, their numbers continue to amaze scientists.

A kind of RNA known as microRNA is now believed to regulate the activity of a third of human protein encoding genes. The RNA could be the answer for puzzles like why the worm C elegans has almost same number of protein-coding genes as the human. The difference is that the RNA plays more diverse roles in each organism.

Calling it a kind of revolution in biology, Nobel laureate David Baltimore spoke of the hypothesis that suggests the form of life that first appeared on earth had no DNA but was coded in RNA. The evidence is all gone but for some remnants like the RNA virus where the RNA constitutes the genetic material implying it is a leftover from the earlier role of RNA.

So also the ribosome where all proteins are made is scaffolded by RNA that also does key catalysis, and the microRNAs that regulate protein amounts from the messenger RNA, all these pointed to a bigger role for RNA, he said.

He was addressing a packed audience at the J N Tata auditorium where he delivered the Cell press-TnQ lecture on 'microRNAs in inflammation and cancer'.

The microRNAs are almost 1000 in number in the human genome, he said, and have multiple targets and can regulate 30 percent of the protein coding genome. Its role in biological processing ranges from tissue differentiation and organ development to apoptosis (cell death) and insulin secretion.

However they have been linked to cancer and even infections. Without the microRNA the protein it controls is produced in large numbers. And if there is too much of the RNA the protein is under-produced. In either instance it could result in cancer as was shown in his work with two kinds of microRNAs on mice.

Studying RNAs through the backdoor by looking at certain transcription factors, Baltimore noted how the factor is involved in the first line of defence to any inflammation. But chronic inflammation as in old people and heart ailments or with cancer can destroy the response. The inactivation of this factor by the microRNA is important.

That was what led him on.

There are important clues to cancer in the role of microRNAs as regulators of genes but much more is not known about their roles.

Research work

Starting with mammalian genetics, his early investigations examined the molecular processes underlying the ability of poliovirus to infect cells. This led him to work on other RNA viruses and then to a consideration of how cancer-causing RNA viruses manage to infect and permanently alter a healthy cell. He identified the enzyme reverse transcriptase in the virus particles, thus providing strong evidence for a process of RNA to DNA conversion, the existence of which had been hypothesized some years earlier. Baltimore and Howard Temin (with Renato Dulbecco, for related research) shared the 1975 Nobel Prize in Physiology or Medicine for their discovery.