The SAID domain promotes ubiquitination and endocytosis of a heterologous protein.

<p>(A–D) Confocal images of S2 cells transfected with CFP-tagged Fz2 (A), Fz2-SAID fusion (FS in B), Fz2-SAID with either the phospho-mimetic (FS-SD in C), or the phosphorylation deficient (FS-SA in D) mutations together with YFP-Rab5. Addition of the wild type or phosphorylation deficient but not the phospho-mimetic form of SAID to Fz2 increased its endocytosis and colocalization with Rab5. (E) Myc-tagged Fz2, FS-SA, and FS-SD were transfected into S2 cells with HA-Ub. Cell lysates were immuno-precipitated (IP) with anti-Myc antibody, followed by Western blot with anti-HA (top panel) and anti-Myc (bottom panel) antibodies.