Here we show that ER-alpha proteins with single or double lysine mutations of these motifs (including K303R, a cancer-associated mutant) are resistant to inhibition by BRCA1, even though the mutant ER-alpha proteins retain the ability to bind to BRCA1.
The fact that the mutation was not found leads us to believe that this mutation is absent from most cells in invasive carcinomas and furthermore that the major expression product of the ER-alpha gene in cancers does not contain the K303R mutation.