Figure 1: Distribution of BRCA1 mutations and BRCA1 protein in cells derived from BRCA1 mutation carriers.

(a) Cells were derived from skin punch biopsies and prophylactic mastectomies performed on BRCA1 mutation carrying women. (b) Western blot analysis of total BRCA1 protein levels in BRCA1^mut/+ and BRCA1^+/+ HMEC lines. Equivalent amounts of whole-cell lysate (prepared in NETN300) were electrophoresed, blotted and the blots probed with an anti-BRCA1 monoclonal Ab (SD118). GAPDH served as a loading control. (c) Western blot analysis of BRCA1 protein levels in the nuclear fraction of BRCA1^mut/+ and BRCA1^+/+ fibroblast strains. Cells were pre-lysed in pre-extraction buffer (PEB, details in Materials and Methods), and the pellet was re-suspended in NETN400 buffer to prepare a nuclear extract. The intense BRCA1 band in 47 (185delAG, marked by an asterisk) is likely the previously discovered truncated product of this mutant allele⁴⁵. A non- specific band served as the loading control.