This domain has been annotated as Rac1-binding domain [1, 2]. It can be found in human CYRIA/CYRIB and at the N terminus of CYFIP1/2 [3]. CYFIP proteins are known RAC1 effectors that stimulate actin polymerization [3]. In mice, CYRIB (also known as CYRI or FAM49B) negatively regulates RAC1-driven cytoskeletal remodelling and plays a role in restricting infection mediated by Mycobacterium tuberculosis and Listeria monocytogenes [3].

1: CYRI/ Fam49 Proteins Represent a New Class of Rac1 Interactors. Whitelaw JA, Lilla S, Paul NR, Fort L, Zanivan S, Machesky LM; Commun Integr Biol. 2019;12:112-118. PMID:31413787

2: Fam49/CYRI interacts with Rac1 and locally suppresses protrusions. Fort L, Batista JM, Thomason PA, Spence HJ, Whitelaw JA, Tweedy L, Greaves J, Martin KJ, Anderson KI, Brown P, Lilla S, Neilson MP, Tafelmeyer P, Zanivan S, Ismail S, Bryant DM, Tomkinson NCO, Chamberlain LH, Mastick GS, Insall RH, Machesky LM; Nat Cell Biol. 2018;20:1159-1171. PMID:30250061

3: CYRI/FAM49B negatively regulates RAC1-driven cytoskeletal remodelling and protects against bacterial infection. Yuki KE, Marei H, Fiskin E, Eva MM, Gopal AA, Schwartzentruber JA, Majewski J, Cellier M, Mandl JN, Vidal SM, Malo D, Dikic I; Nat Microbiol. 2019;4:1516-1531. PMID:31285585