Fig. 1. Surface expression of MPR300 in control (ct) and µ1A-deficient cells (µ1A–/–). Cells were rapidly cooled to 0°C and biotinylated. Biotinylated proteins were precipitated with streptavidin-agarose from 300-500 µg of cell extract proteins. Precipitates of biotinylated proteins and 100 µg of total protein extracts were analyzed in western blots by anti-MPR300 antibodies. Signals were quantified by densitometry and normalized for the protein content (see Materials and Methods for experimental details).