RNA switches the higher-order structure of DNA.

By the direct observation of single duplex DNA molecules by fluorescence microscopy, we found that RNA molecules have the potential to change discretely the higher-order structure of individual DNA molecules between the compact and elongated states. We performed an experiment with a linear giant DNA (T4 DNA, 166 kbp) and a circular DNA (cosmid vector, 42 kbp), and examined the effect of single-strand RNA on their conformations under a physiological concentration of spermidine. Individual DNA chains compacted by spermidine were elongated in an abrupt manner with an increase in the RNA concentration. This finding is discussed in view of the effect of the interplay between the dynamics of chromosomal DNA and the production of RNA in the cytoplasmic environment.