ISOLATION AND CHARACTERIZATION OF GLYCOGEN-SYNTHASE IN DICTYOSTELIUM-DISCOIDEUM

We have partially purified the protein and isolated the glcS gene for glycogen synthase in Dictyostelium. glcS mRNA is present throughout de velopment and is the product of a single gene coding for 775 amino aci ds, with a predicted molecular mass of 87 kD. The sequence is highly s imilar to glycogen synthase from human muscle, yeast, and rat liver, d iverging significantly only at the amino and carboxy termini. Phosphor ylation and UDPG binding sites are conserved, with K-m values for UDPG being comparable to those determined for other organisms, but in vitr o phosphorylation failing to convert between the G6P-dependent (D) and -independent (I) forms. Enzyme activity is relatively constant throug hout the life cycle: the I form of the enzyme isolates with the solubl e fraction in amoebae, switches to the D form, becomes pellet-associat ed during early development, and finally reverts during late developme nt to the I form, which again localizes to the soluble fraction. Delet ion analysis of the promoter reveals a GC-rich element which, when del eted, abolishes expression of glcS. (C) 1996 Wiley-Liss, Inc.