Signal-Transducing G-Proteins in Dictyostelium Discoideum
Most of the studies on signaltransduction and the role of G-proteins therein have been done on mammalian cells. This brings about several disadvantages, such as laborious growth conditions non-homogeneous material and the use of highly specialized cells. The use of tumor cell lines brings the risk of using cells in which especially the signaltransduction pathways are somehow impaired. Using micro-organisms can overcome many of these disadvantages. In our studies we use the cellular slime mold Dictyostelium discoideum which is an easy to grow haploid organism with a simple life cycle. The fact that it is haploid makes it easier to perform both classical as well as molecular genetics. Dictyostelium discoideum is a soil living organism which feeds on bacteria during its vegetative stage. Upon food deprivation it enters a social stage in which cells aggregate into multicellular structures in response to excreted cAMP. Subsequently differentiation to two different cell types (i.e. spores and stalk cells) takes place (Schaap 1986) . In the aggregative stage cAMP elicits several cellular responses which are thought to be mediated by two types of cAMP surface receptors, the A sites which exist in a low (AL) and a high (AH) affinity form and the B sites of which three kinetic forms can be distinguished. A fast dissociating form (BF) a slower dissociating form (Bs) and a very slowly dissociating form (Bss) (Van Haastert, et al. 1986) .
KeywordsAdenylate Cyclase Pertussis Toxin GTPase Activity Dictyostelium Discoideum Cellular Slime Mold
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