Phg1p is a nine-transmembrane protein superfamily member involved in Dictyostelium adhesion and phagocytosis

To identify the molecular mechanisms involved in phagocytosis, we generated random insertion mutants of Dictyostelium discoideum and selected two muta nts defective for phagocytosis. Both represented insertions in the same gen e, named PHG1. This gene encodes a polytopic membrane protein with an N-ter minal lumenal domain and nine potential transmembrane segments. Homologous genes can be identified in many species; however, their function is yet to be elucidated. Disruption of PHG1 caused a selective defect in phagocytosis of latex beads and Escherichia coli, but not Klebsiella aerogenes bacteria . This defect in phagocytosis was caused by a decrease in the adhesion of m utant cells to phagocytosed particles. These results indicate that the Phg1 protein is involved in the adhesion of Dictyostelium to various substrates , a crucial event of phagocytosis and demonstrate the usefulness of a genet ic approach to dissect the molecular events involved in the phagocytic proc ess.