| The polyene antibiotic pimaricin inhibits the growth of the cellular slime mold Dictyostelium discoideum. This provides a selection for mutants which have the ability to grow on this drug. We have been able to select pimaricin resistant mutations in three different genetic backgrounds. The mutations fall into at least eight complementation groups. By selecting for mutants on pimaricin containing agar two classes of mutations have been found, those that produce an altered sterol, or sterols, in the mutants, and those that have no effect on the sterol composition of the mutant strain. Although both classes of mutants are of interest for studies of D. discoideum growth and development, the mutants containing an altered, or altered sterols are most immediately accessible for biochemical analysis. The altered sterol is presumed to be a precursor of the natural sterol end product that either binds the drug less efficiently than the wild-type, or in some other way inhibits the lethal effect of the drug-sterol interaction. These mutations have a variety of effects on the biology of the mutant strains. This study shows that the sterol alterations play the critical role in determining the mutant phenotypes. By experimentally reverting the mutant sterol to wild-type, without reverting the mutant gene to wild-type, it has been shown that all accompanying mutant phenotypes revert to wild-type.;As a byproduct of this work we have made inroads into the sterol biosynthetic pathway of D. discoideum which had been unexplored, and into how the sterol biosynthetic pathway is regulated. |
