doi:10.1038/nindia.2008.179 Published online 11 April 2008
A new study involving the poorly studied transcription by the enzyme RNA polymerase III, one of the three enzymes that help express the genes in our body, has found that its regulation is linked to the structure of chromatin, the nucleoprotein complex packed inside the nucleus of the cell. The study is important as it sheds new light on the little known functioning of RNA pol III in chromatin context.
Genes are expressed by 'transcription' or copying of DNA parts into the RNA. In higher organisms, three enzymes called RNA polymerases carry out this process. RNA polymerase (pol) II synthesizes the messenger RNA carrying the genetic code, which can be translated into a protein. The other two polymerases make the RNAs required for the synthesis of the ribosomes, the tiny workstations where translation takes place as well as other small RNAs required for the protein synthesis.
Regulation of activity of pol II-transcribed genes results in the regulated production of individual proteins, the major work horses of the cells. Regulation of pol I and III activity can affect the global protein synthesizing capacity of the cells. "As compared to pol II, pol III transcription has not received much attention till now though it contributes a very important pool of RNAs to the cell," says one of the researchers Purnima Bhargava.
The study by researchers from the Centre for Cellular and Molecular Biology in Hyderabad gives the first ever evidence of involvement of an ATP-dependent chromatin remodeler and a histone variant in vivo in regulating transcription of a gene transcribed by RNA pol III. It also provides the molecular details of the in vivo changes in the upstream region of a pol III-transcribed gene, while they are known to have only intragenic promoter elements.