A temperature-sensitive adenylyl cyclase mutant of Dictyostelium

Dictyostelium development starts with the chemotactic aggregation of up to 10⁶ amoebae in response to propagating cAMP waves. cAMP is produced by the aggregation stage adenylyl cyclase (ACA) and cells lacking ACA (aca null) cannot aggregate. Temperature-sensitive mutants of ACA were selected from a population of aca null cells transformed with a library of ACA genes, a major segment of which had been amplified by error-prone PCR. One mutant (tsaca2) that can complement the aggregation null phenotype of aca null cells at 22°C but not at 28°C was characterized in detail. The basal catalytic activity of the enzyme in this mutant was rapidly and reversibly inactivated at 28°C. Using this mutant strain we show that cell movement in aggregates and mounds is organized by propagating waves of cAMP. Synergy experiments between wild-type and tsaca2 cells, shifted to the restrictive temperature at various stages of development, showed that ACA plays an important role in the control of cell sorting and tip formation.