Attempts to isolate mutants of Dictyostelium discoideum which express alpha-mannosidase-2 constitutively

Evidence was sought for a gene-specific negative regulatory element of Dictyostelium discoideum similar to the repressor/operator systems that control some operons in prokaryotes and their viruses. Mutants of D. discoideum that constitutively express the stage-specific enzyme alpha-mannosidase-2 could provide such evidence. Reconstruction experiments demonstrated that the screening technique developed would detect mutants of that type. Over 2 x 10(5) survivors of heavily mutagenized cell populations were grown and their progeny tested. No mutants of the desired type were obtained. The possible implications of this finding are discussed.