The effect of DMSO on natural DNA conformation in enhancing transcription

In the presence of 5% dimethylsulfoxide, 2.5 fold increase in vitro RNA synthesis rate by E. coli RNA polymerase was observed as superhelical pBR322 DNA was used as template. The effect of DMSO on DNA conformation was studied by: [i] measuring the dissociation constant of EtBr-DNA complex and the maximum EtBr binding site of EtBr in DNA which changed from 7.52 X 10(-7) M and 0.18 site per nucleotide to 9.61 X 10(-7) M and 0.156 site per nucleotide respectively when 10% DMSO was supplemented; and [ii] the increase of average linking number of pBR322 DNA in DMSO solution with topoisomerase I reaction. These results suggest that the stimulation of RNA synthesis may be caused by the easier initiation and elongation of RNA synthesis at some locally loosen regions of DNA affected by another torsionally more twisted counterpart regions in the DMSO microenvironment.