Long-term Structural Change in Plasmid DNA

Long-term stability of plasmid DNA (pDNA) conformations is critical in many research areas, especially those concerning future gene therapy. Despite its importance, the timeevolution of pDNA structures has rarely been studied at a molecular resolution. Here, the time-evolution of pDNA solutions spanning four years was observed with atomic force microscopy (AFM). The AFM data show that the pDNA molecules evolved from isolated supercoiled structures; to aggregated supercoiled structures; to thin, branched network structures; and finally to wider, branched network structures. Additional topographical analysis of the AFM data suggests the actions of residual proteins could be the main mechanism for the structural changes in our laboratory prepared pDNA.