This BRCT domain, a BRCA1 C-terminus region, is found on many RAP1 proteins, usually at the very N-terminus. The function in human at least of a BRCT is to contribute to the heterogeneity of the telomere DNA length, but that may not be its general function, which remains unknown [1,2].

1: A conserved motif within RAP1 has diversified roles in telomere protection and regulation in different organisms. Chen Y, Rai R, Zhou ZR, Kanoh J, Ribeyre C, Yang Y, Zheng H, Damay P, Wang F, Tsujii H, Hiraoka Y, Shore D, Hu HY, Chang S, Lei M; Nat Struct Mol Biol. 2011;18:213-221. PMID:21217703

2: Identification of the functional domains of the telomere protein Rap1 in Schizosaccharomyces pombe. Fujita I, Tanaka M, Kanoh J; PLoS One. 2012;7:e49151. PMID:23133674

3: Structure of the BRCT repeat domain of MDC1 and its specificity for the free COOH-terminal end of the gamma-H2AX histone tail. Lee MS, Edwards RA, Thede GL, Glover JN; J Biol Chem. 2005;280:32053-32056. PMID:16049003

4: Molecular basis for the association of microcephalin (MCPH1) protein with the cell division cycle protein 27 (Cdc27) subunit of the anaphase-promoting complex. Singh N, Wiltshire TD, Thompson JR, Mer G, Couch FJ; J Biol Chem. 2012;287:2854-2862. PMID:22139841