In the early 70s it was pointed out that in order to keep track of the information required to proof read (ie, check for and correct errors), the cell had to have processes that dissipate (waste) energy, otherwise they would contradict the second law of thermodynamics which states that unless energy is supplied, disorder (ie, lack of information) tends to increase. Experiments have suggested a number of possible mechanisms by which this might occur, but it is difficult to figure out which, if any, is the primary one, so exactly how these processes occur remains a mystery.

Liverpool's paper, published today in Physical Review Letters, develops a mathematical model for proofreading in the transcription process, based on the fact that the RNAP does not move only in one direction along the DNA, but often makes random backward excursions as it transcribes the gene. The model shows how these 'backtracks' can improve the accuracy of transcription, and predicts the dependence of the probability of finding errors on the backtracking dynamics.

The results of the model suggest future experiments which can be used to discriminate between the different possible mechanisms. They should also shed light on error correction in other biological processes such as the translation of RNA to protein.

Backtracking and Proofreading in DNA Transcription. Margaritis Voliotis, Netta Cohen, Carmen Molina-Par?­s, and Tanniemola B. Liverpool. Physical Review Letters, 26 June 2009, Volume 102, Number 2. Published online ahead of print 22 June 2009.

Dr Tanniemola Liverpool

bris.ac/