Characterization and genetic mapping of modA. A mutation in the post-translational modification of the glycosidases of Dictyostelium discoideum.

We have isolated a mutant of Dictyostelium discoideum, M31, which produces a reduced number of alpha-mannosidase-1 molecules per cell during the developmental program of the organism. We find that several of the glycosidases, a group of lysosomal proteins produced by D. discoideum, are altered in strain M31 and that this strain produces a reduced level of at least three of these activities. These enzymes do not share a common protein subunit but are known to share a common antigenic determinant which is, in part, carbohydrate in nature. In the wild type parent of M31, alpha-mannosidase-1 is modified by the addition of mannose and glucosamine (probably as N-acetylglucosamine) in the molar ratio of 5:2. alpha-Mannosidase-1 was also found to contain phosphoserine/phosphothreonine residues. alpha-Mannosidase-1 and other glycosidases are electrophoretically less negative when isolated from strain M31 than when isolated from wild type cells. The mutation present in M31, modA, appears to affect posttranslational modification, modA is a recessive mutation which we map onto linkage group I.