Photoinduced conformational changes in DNA by poly(vinyl alcohol) carrying a malachite green moiety for protecting DNA against attack by nuclease.

Light is a highly advantageous means of specific cell targeting. Though targeted gene delivery is an important characteristic of an ideal delivery vehicle, there has been little effort to develop a photoresponsive vector. Among nonviral vectors, cationic substances interact effectively with negatively charged DNA. With this property in mind, we designed copolymers of poly(vinyl alcohol) carrying a malachite green moiety (PVAMG) with different molecular weights. Though PVAMG has no affinity for DNA in the absence of light, it undergoes photoionization in the presence of light to afford cationic DNA binding sites. The DNA-PVAMG complex was investigated with respect to DNA conformational changes and its protective nature, which are important properties for nonviral vectors. PVAMG irradiation promoted DNA conformational transitions from coils to partial globules to compacted globules. The complex had a protective effect against DNase I after PVAMG irradiation, while DNA was degraded under dark conditions. The effect on DNA transition and the protective nature were sensitive to the molecular weight of PVAMG. The data regarding binding constants and binding mode provided insight into the structure of the DNA-PVAMG complex. To withstand DNase I attacks, complexation results in the compaction of DNA, which is further covered with PVAMG.