High Quality Content by WIKIPEDIA articles! Dock4, (Dedicator of cytokinesis 4) also known as DOCK4, is a large (~190 kDa) protein involved in intracellular signalling networks. It is a member of the DOCK-B subfamily of the DOCK family of guanine nucleotide exchange factors (GEFs) which function as activators of small G proteins. Dock4 activates the small G proteins Rac and Rap1.