AcrF3, a protein encoded by gene 35 from phage JBD5, has been reported to specifically inhibit the Cas3 protein of the P. aeruginosa PA14 strain (PaCas3) and to counteract the type I-F CRISPR-Cas system [1]. AcrF3 eluted as a dimer in gel-filtration chromatography [1]. In the complex structure, AcrF3 binds to PaCas3 at a ratio of 2:1, suggesting that AcrF3 functions as a homodimer that inhibits PaCas3 [1]. A single AcrF3 molecule has a two-layer architecture with six alpha-helices [1].

1: Structural basis of Cas3 inhibition by the bacteriophage protein AcrF3. Wang X, Yao D, Xu JG, Li AR, Xu J, Fu P, Zhou Y, Zhu Y; Nat Struct Mol Biol. 2016;23:868-870. PMID:27455460

2: A CRISPR evolutionary arms race: structural insights into viral anti-CRISPR/Cas responses. Wang J, Ma J, Cheng Z, Meng X, You L, Wang M, Zhang X, Wang Y; Cell Res. 2016;26:1165-1168. PMID:27585537