Rhotekin (RTKN) has the evolutionarily conserved RHO GTPase binding domain at its N-terminus and strongly binds to RHOA and RHOC. RTKN also associates with RHOB with a lower affinity and does not bind RAC1 or CDC42 (Reid et al. 1996). Binding of RTKN may inhibit the GTPase activity of RHO GTPases (Fu et al. 2000).