FIGURE 1.

BRCA1 regulates DNA cleavage at a TG site. A–C, proliferating MCF-7 cells were transiently transfected overnight with vehicle, wild-type BRCA1 (WTBRCA1), or empty pcDNA3 vector, washed, and allowed to recover for several hours prior to assay. Nuclear extracts were prepared, and 30-μg aliquots were tested for their ability to incise duplex oligonucleotides (oligo) containing a TG lesion, using the corresponding wild-type duplex oligonucleotide as a control. A shows a representative DNA gel; B shows the quantitative extents of cleavage, expressed as means ± S.E. of three independent experiments. The protein levels of BRCA1, NTH1, and α-actin for the different transfection conditions are shown in C. D–F, MCF-7 cells were treated with BRCA1-siRNA (100 nm), control (CON)-siRNA, or vehicle only and assayed for incising activity at a TG site as described above. D shows a representative DNA gel; E shows the quantitative extent of cleavage. The BRCA1, NTH1, and actin protein levels for the different treatment conditions are shown in F. B and E, an asterisk represents a statistically significant difference (p < 0.05, two-tailed t test). nt, nucleotide.