The function of BRAP (BRCA1 associated protein, ENSG00000089234) is as follows. Negatively regulates MAP kinase activation by limiting the formation of Raf/MEK complexes probably by inactivation of the KSR1 scaffold protein. Also acts as a Ras responsive E3 ubiquitin ligase that, on activation of Ras, is modified by auto-polyubiquitination resulting in the release of inhibition of Raf/MEK complex formation. May also act as a cytoplasmic retention protein with a role in regulating nuclear transport. {ECO:0000269|PubMed:14724641, ECO:0000303|PubMed:10777491}.