Abstract
The Dictyostelium discoidin genes are induced in bacteria-grown cells shortly before the onset of development but are also highly expressed during growth in axenic medium. We here show that axenically growing cells strongly respond to the extracellular signal folate by suppressing discoidin synthesis while cell growth and development is not substantially affected. Repression occurs via two previously identified promoter elements, the dIE and the dAXE. Removal of the signal molecules or setting cells up for development results in rapid reactivation of the promoter. Based on this observation, we constructed the transformation vector pVEII and describe a convenient method which allows for controlled expression of a gene of interest in growing cells and also for external modulation in early development. Deletion constructs of the discoidin promoter can be used in addition to vary transcriptional activity over about one order of magnitude.