THE CYTOSOLIC GLYCOPROTEIN FP21 OF DICTYOSTELIUM-DISCOIDEUM IS ENCODED BY 2 GENES RESULTING IN A POLYMORPHISM AT A SINGLE AMINO-ACID POSITION

FP21 is a glycoprotein within the cytosolic compartment of Dictyosteli um which carries an unusual carbohydrate modification(s) including the sugars fucose, galactose and Iv-acetylglucosamine. The soluble pool o f FP21 from crude extracts resolves chromatographically into two fract ions that differ in their glycosylation. Previous gene-mapping studies indicating the existence of two loci suggested that the FP21 fraction s might be encoded by different genes. To address this issue, the two genes were cloned and sequenced, leading to the prediction that the pr otein products would differ by only a single amino acid, Ser or Ala, a t codon 39. Protein sequence data on CNBr fragments of purified FP21 s howed that both gene products are found in both fractions of the solub le pool. After further purification, the two fractions were no longer chromatographically resolvable, and there was no evidence for charge h eterogeneity as determined by 2-D gel electrophoresis of whole cells. Thus, the initial separation of the different soluble subpopulations o f this protein appears to be due to distinct molecular complexes, poss ibly related to differential glycosylation, and is not the result of t he genetically-encoded amino acid polymorphism. (C) 1997 Elsevier Scie nce B.V.