A transfection reporter for the prevention of false-negative results in molecular beacon experiments

Facile preparation of a fluorescent probe to detect the cellular ability of nucleotide excision repair

We previously developed a method to detect the cellular ability of nucleotide excision repair, which functions to remove UV-induced lesions in DNA, using a plasmid-type fluorescent probe. A drawback to the popular use of this method was that the oligonucleotide containing the (6-4) photoproduct, which was used as a primer in the plasmid preparation, must be synthesized chemically. In this study, we prepared the probe using a post-synthetically UV-irradiated oligonucleotide as the primer. Transfection of cells demonstrated that this probe detected the repair ability of the cells in the same manner as the original probe.

Fluorescence detection of cellular nucleotide excision repair of damaged DNA

To maintain genetic integrity, ultraviolet light-induced photoproducts in DNA must be removed by the nucleotide excision repair (NER) pathway, which is initiated by damage recognition and dual incisions of the lesion-containing strand. We intended to detect the dual-incision step of cellular NER, by using a fluorescent probe. A 140-base pair linear duplex containing the (6-4) photoproduct and a fluorophore-quencher pair was prepared first. However, this type of DNA was found to be degraded rapidly by nucleases in cells. Next, a plasmid was used as a scaffold. In this case, the fluorophore and the quencher were attached to the same strand, and we expected that the dual-incision product containing them would be degraded in cells. At 3 h after transfection of HeLa cells with the plasmid-type probes, fluorescence emission was detected at the nuclei by fluorescence microscopy only when the probe contained the (6-4) photoproduct, and the results were confirmed by flow cytometry. Finally, XPA fibroblasts and the same cells expressing the XPA gene were transfected with the photoproduct-containing probe. Although the transfer of the probe into the cells was slow, fluorescence was detected depending on the NER ability of the cells.