Heterodimer with
BARD1 (PubMed:11573085, PubMed:12890688, PubMed:14976165). Part of the
BRCA1-associated genome surveillance complex (BASC), which contains
BRCA1,
MSH2,
MSH6,
MLH1,
ATM,
BLM,
PMS2 and the
MRE11-
RAD50-
NBN protein (MRN) complex (PubMed:10783165). This association could be a dynamic process changing throughout the cell cycle and within subnuclear domains (PubMed:10783165). Component of the
BRCA1-A complex, at least composed of
BRCA1,
BARD1,
UIMC1/RAP80,
ABRAXAS1,
BRCC3/
BRCC36,
BABAM2 and
BABAM1/NBA1 (PubMed:19261746, PubMed:19261748, PubMed:19261749, PubMed:20351172). Interacts (via the BRCT domains) with
ABRAXAS1 (phosphorylated form); this is important for recruitment to sites of DNA damage (PubMed:17525340, PubMed:17643121, PubMed:17643122, PubMed:24316840, PubMed:26778126, PubMed:23269703). Can form a heterotetramer with two molecules of
ABRAXAS1 (phosphorylated form) (PubMed:26778126). Component of the
BRCA1-
RBBP8 complex (PubMed:16101277). Interacts (via the BRCT domains) with
RBBP8 ('Ser-327' phosphorylated form); the interaction ubiquitinates
RBBP8, regulates
CHEK1 activation, and involves
RBBP8 in
BRCA1-dependent G2/M checkpoint control on DNA damage (PubMed:16818604, PubMed:9811458). Associates with RNA polymerase II holoenzyme (PubMed:9662397). Interacts with
SMC1A, COBRA1,
DCLRE1C,
CLSPN (PubMed:11877377, PubMed:15096610, PubMed:15456891). Interacts with
CHEK1,
CHEK2,
BAP1,
BRCC3,
AURKA,
UBXN1 and
PCLAF (PubMed:10724175, PubMed:11836499, PubMed:14636569, PubMed:14990569, PubMed:20351172, PubMed:21673012). Interacts (via BRCT domains) with
BRIP1 (phosphorylated form) (PubMed:11301010, PubMed:15133502, PubMed:21473589). Interacts with
FANCD2 (ubiquitinated form) (PubMed:11239454). Interacts with
H2AFX (phosphorylated on 'Ser-140') (PubMed:12419185). Interacts (via the BRCT domains) with
ACACA (phosphorylated form); the interaction prevents dephosphorylation of
ACACA (PubMed:12360400, PubMed:16326698, PubMed:16698035, PubMed:18452305). Part of a BRCA complex containing
BRCA1,
BRCA2 and
PALB2 (PubMed:19369211). Interacts directly with
PALB2; the interaction is essential for its function in HRR (PubMed:19369211, PubMed:28319063). Interacts directly with
BRCA2; the interaction occurs only in the presence of
PALB2 which serves as the bridging protein (PubMed:19369211). Interacts (via the BRCT domains) with
LMO4; the interaction represses the transcriptional activity of
BRCA1 (PubMed:11751867). Interacts (via the BRCT domains) with
CCAR2 (via N-terminus); the interaction represses the transcriptional activator activity of
BRCA1 (PubMed:20160719). Interacts with
EXD2 (PubMed:26807646). Interacts (via C-terminus) with
DHX9; this interaction is direct and links
BRCA1 to the RNA polymerase II holoenzyme (PubMed:9662397).
UniProt