contact sites A

Developmentally-regulated adhesion sites that appear on the ends of aggregation-competent Dictyostelium discoideum (see Acrasidae) - at the stage when the starved cells begin to come together to form the grex. Originally detected by the use of Fab fragments of polyclonal antibodies, raised against aggregation-competent cells and adsorbed against vegetative cells, to block adhesion in EDTA-containing medium. (Cell-cell adhesion mediated by contact sites A, unlike that mediated by contact sites B, is not divalent cation-sensitive). The fact that a mutant deficient in csA behaves perfectly normally in culture is puzzling.