The Influence of the Cellular Environment on Z-DNA Formation

Abstract

In the cell, chemically diverse solutes known as osmolytes accumulate in response to environmental stresses. To add to the understanding of how the environment inside a cell affects nucleic acid folding and function, we investigated the influence of cosolutes on the transition from B-DNA to Z-DNA in model DNA duplexes. Distinct from the familiar right-handed BDNA helical conformation, Z-DNA is a left-handed double helical structure with its phosphodiester backbone arranged in a zig-zag pattern that is unique to Z-DNA. Moreover, due to the correlation between Z-DNA formation potential and regions of active transcription, ZDNA is believed to serve a vital role in the transcription process. Previous literature has shown that divalent metal ions such as Ca2+ and Mg2+ can promote the formation of Z-DNA in vitro and previous studies from our lab have shown that the presence of osmolytes enhances the formation of Z-DNA, significantly decreasing the in vitro [Na+] required for the transition. In our latest experiments, we examined the combination of divalent ions and osmolytes and its influence on the B-Z transition. We utilized circular dichroism (CD) spectroscopy to monitor the B-Z transition in a divalent ion background in the presence and absence of a model osmolyte, PEG 200. Our results thus far suggest that PEG 200 greatly enhances the formation of Z-DNA in the presence of Mg2+ as compared with Na+ alone and significantly decreases the [Mg2+] required for folding in vitro. Our results with Ca2+ thus far suggest that its folding of Z-DNA is similarly enhanced by PEG 200 and that the effect of metal ions on Z-DNA formation can be observed in vivo.