Sap-1 dimerizes through its extracellular domain Full-size image (23 K) Fig. 2. Sap-1 forms homodimers. Left panel: cells were transfected to co-express full-length, His6-tagged Sap-1 extracellular domains (Δ-intra) plus various HA-tagged Sap-1 constructs. HA-tagged protein was immunoprecipitated, a