The mammalian and Drosophila pocket protein families. The pocket protein family in mammals consists of Rb, p107 and p130, and in Drosophila contains RBF and RBF2. The pocket domain, responsible for most protein–protein interactions, consists of two conserved sequences, A and B. The spacer region between A and B is conserved between p107 and p130 (yellow box), and can bind to cyclin/cdk complexes. The activity of Rb proteins is controlled by phosphorylation at numerous phosphorylation sites (indicated for Rb and RBF by *).