This phospho-peptide is derived from human acetyl-CoA carboxylase 1 (ACC1) residue 1258-1271. ACC1 is an enzyme with crucial roles in de novo fatty acid biosynthesis and cancer cell survival. This enzyme catalyzes the first and rate-limiting step of de novo fatty acid biosynthesis. Many lines of evidence suggest that up-regulation of fatty acid biosynthesis is required for carcinogenesis, as more than 90% of the lipids are synthesized through de novo lipogenesis in cancer cells. BRCA1 significantly reduces the rate of fatty acid biosynthesis when complexed with ACC1. The crystal structure of human BRCA1 and this phospho-peptide provides structural evidence for direct interactions between BRCA1 and ACC1, which may be the molecular basis for the regulation of lipid biosynthesis by BRCA1.