Interactions of fluorescent dye SYBR Green I with natural and 7-deazaguanine-modified DNA studied by fluorescence and electrochemical methods
SYBR Green I (SG) is a fluorescent dye applied in various techniques of DNA analysis, including fluorescent staining of electrophoretic gels, quantitative polymerase chain reaction, etc. SG binds selectively to double-stranded DNA via intercalation and minor groove interactions, resulting in a considerable enhancement of fluorescence of the dye. Modification of DNA by partial or full replacement of natural purine nucleobase guanine (G) with its synthetic analog 7-deazaguanine (G*) or its derivatives was shown to cause the SG fluorescence quenching. In this paper, we present a comparative study of interactions of SG with natural DNA fragments and with DNA fragments modified with G* by means of fluorescence and electrochemical methods. Competition between unmodified (forming strongly fluorescent complex with SG) and fully G*-modified (not contributing significantly to overall fluorescence signal) DNA fragments for the dye was studied via changes in the fluorescence intensity. In addition, association interactions of natural or G*-modified DNA with SG in solution were monitored by adsorptive transfer stripping square wave voltammetry at a pyrolytic graphite electrode using a signal of SG electrooxidation. We show that SG binds both natural and G*-modified DNA with similar apparent affinity and selectivity for the double-stranded DNA. [GRAPHICS] .