Specific GEF for RhoA activation. Does not activate RAC1 or CDC42. Regulates vascular smooth muscle contractility. Negatively regulates excitatory synapse development by suppressing the synapse-promoting activity of EPHB2. Interacts with EPHB2 (By similarity). Interacts with EPHA4. Expressed exclusively in dendrites of the developing hippocampus. Expressed in the vascular smooth muscle of coronary artery. Phosphorylated on tyrosine residues upon EFNA1 stimulation. EPHB2-dependent phosphorylation at Tyr-353 triggers UBE3A-mediated ubiquitination (By similarity). Ubiquitinated; UBE3A-mediated ubiquitination and degradation by the proteasome promotes EFNB1-dependent synapse formation. Extended N-terminus.