Yeast release SDF-2–like material. (A) Amino acid sequence of the AcbA homologues in S.cerevisiae, D. discoideum, and Homo sapiens are aligned. (B) The assay for the activity of Acb1. Yeast cells were starved for the time indicated. The cells were separated from the medium by low speed centrifugation and lysed. The lysates were used for detection of the intracellular levels of Acb1 and the control protein 3-phosphoglycerate kinase (Pgk1). The medium was processed to concentrate Acb1 activity, which was then tested for its ability to sporulate D. discoideum KP cells and quantified. (C) Developed KP cells were incubated with buffer in which yeast had been starved for 4 h and the number of spores counted 1 h later. (D) Protein levels were assessed by Western blotting the yeast cell lysates with an anti-Pgk1p (3-phosphoglycerate kinase) antibody, which is a cytosolic protein used as a control, and anti-Acb1. Anti-Flag antibody shows expression of the tagged version of Acb1-Flag. (E) Time course of secretion. Yeast cells were starved, and samples were taken every 30 min up to 4 h. The buffer was assayed for SDF-2–like activity. The data show an average of three experiments.