A NEW COLLECTION OF THERMOSENSITIVE ENDOCYTOSIS MUTANTS IN THE CELLULAR SLIME-MOLD DICTYOSTELIUM-DISCOIDEUM

We used a photoactivatable fluid-phase marker to isolate a new collect ion of thermosensitive endocytosis mutants in the cellular slime mold Dictyostelium discoideum. All the strains were thermosensitive for gro wth on bacteria or axenic medium at 27 degrees C. Initial rates of end ocytosis rapidly decreased upon incubation at the restrictive temperat ure, but surprisingly most of the strains showed a transient recovery of activity with prolonged exposure to 27 degrees C. Endocytosis and e xocytosis activities were uncoupled for some of the cell lines at 27 d egrees C whereas the others had to be shifted to 29 degrees C. Further molecular analysis of these mutants could lead to the discovery of ne w proteins involved in endocytosis and its regulation.