The Central Region of BRCA1 Binds Preferentially to Supercoiled DNA

Abstract BRCA1 is a multifunctional tumor suppressor protein with implications in regulating processes such as cell cycle, transcription, DNA repair, and chromatin remodeling. The function of BRCA1 likely involves interactions with a vast number of proteins and likewise DNA. To this date there is only fragmentary evidence about BRCA1 binding to DNA. In this study, we provide detailed analyses of various BRCA1 protein constructs binding to linear and super-coiled (sc) DNAs. We demonstrate that the central region of human BRCA1 binds strongly to negatively sc plasmid DNA at a native superhelix density, as evidenced by electrophoretic retardation of sc DNA in agarose gels. At relatively low BRCA1:DNA ratios, binding of BRCA1 to sc DNA results in the appearance of one or more retarded DNA bands on the gels. After removal of BRCA1, the original mobility of the sc DNA is recovered. BRCA1 proteins at higher concentrations also bind to the same DNA but in linear state, leading to formation of a smeared retarded b...