RNA 'GUIDED' TO ALTER DNA INSTRUCTIONS

The process of transcribing DNA instructions into proteins has now been found to be a lot smarter than previously imagined.

A detailed comparison of DNA and RNA in human cells has uncovered a surprising number of cases where the corresponding sequences are not, as has long been assumed, identical. The RNA-DNA differences generate proteins that do not precisely match the genes that encode them.

The finding, published May 19, 2011, in Science Express, suggests that unknown cellular processes are acting on RNA to generate a sequence that is not an exact replica of the DNA from which it is copied. Vivian Cheung, the Howard Hughes Medical Institute investigator who led the study, says the RNA-DNA differences (which the researchers casll RDDs), which were found in all 27 individuals whose genetic sequences were analysed, are a previously unrecognised source of genetic diversity that should be taken into account in future studies. They found at least one RDD site in 40% of genes.

Cheung says the particular RNA-DNA discrepancies that they found appear systematic. There are four bases, or letters, that make up the DNA code: A, T, G, and C. The RNA equivalents are A, U, G, and C. In individuals who had RNA-DNA differences at a specific site in the genome, the mismatched bases were always the same. In other words, if the team found a C in the RNA sequence where they expected an A, all individuals who had an RDD at this point also had a C in their RNA sequence--never a G or a U. 'Such uniformity makes us believe that there is a 'code' or 'guide' that mediates the RDDs and they are not random events,' says Cheung. 'And it is important to note that since these RDDs were found with just 27 individuals, they are common.'

Full article in ScienceDaily.