Early endosomal and MVB components are required for Acb1 secretion. (A) Wild-type and deletion mutants for the genes shown were starved for 4 h, and the SDF-2–like activity in the buffer was determined in the bioassay. The data show an average of three experiments. (B) Yeast from A was lysed, and equal amounts were Western blotted with anti-Pgk1 and anti-Acb1 antibody. Deletion mutants are compared with their wild-type isogenic strain (BY4741 or SEY6210). The intracellular levels of Acb1 are not affected in yeast mutants tested in this experiment.