A NOVEL ADENYLYL-CYCLASE DETECTED IN RAPIDLY DEVELOPING MUTANTS OF DICTYOSTELIUM

Disruption of either the RDEA or REGA genes leads to rapid development in Dictyostelium. The RDEA gene product displays homology to certain H2-type phosphotransferases, while REGA encodes a cAMP phosphodiestera se with an associated response regulator. It has been proposed that RD EA activates REGA in a multistep phosphorelay, To test this proposal, we examined cAMP accumulation in rdeA and regA null mutants and found that these mutants show a pronounced accumulation of cAMP at the veget ative stage that is not observed in wild-type cells. This accumulation was due to a novel adenylyl cyclase and not to the known Dictyosteliu m adenylyl cyclases, aggregation stage adenylyl cyclase (ACA) or germi nation stage adenylyl cyclase (ACG), since it occurred in an acaA/rdeA double mutant and, unlike ACG, was inhibited by high osmolarity, The novel adenylyl cyclase was not regulated by G-proteins and was relativ ely insensitive to stimulation by Mn2+ ions. Addition of the cAMP phos phodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) permitted detection of the novel adenylyl cyclase activity in lysates of an acaA /acgA double mutant. The fact that disruption of the RDEA gene as well as inhibition of the REGA-phosphodiesterase by IBMX permitted detecti on of the novel AC activity supports the hypothesis that RDEA activate s REGA.