Fig. 10. Ubiquitin represents an internalization signal for NCAM. (A) Representative images of endocytosed NCAM140 or NCAM180 in the presence or absence of HA-ubiquitin (HA-ubi). B35 cells were co-transfected with HA-ubiquitin and NCAM140 or NCAM180 (second and fourth rows) or with NCAM140 or NCAM180 alone (first and third rows). Endocytosis of NCAM was induced by NCAM-specific antibodies for 60 minutes. HA-ubiquitin was visualized with FITC-conjugated secondary antibodies for identification of HA-ubiquitin-expressing cells, endocytosed NCAM with Cy3-conjugated antibodies and cell surface NCAM using Alexa-Fluor-633-conjugated secondary antibodies. (B) Quantification of endocytosed NCAM or L1 in the presence or absence of HA-ubiquitin. NCAM- or L1-positive vesicles were counted from at least three independent experiments with approximately 15 cells analysed in each experiment. Data are the mean ± s.e.m., ***P<0.0001, **P<0.01, n.s.: not significant.