This family consists of the eukaryotic glycogen synthase proteins GYS1 and GYS2. Glycogen synthase (GS) is the enzyme responsible for the synthesis of -1,4-linked glucose chains in glycogen. It is the rate limiting enzyme in the synthesis of the polysaccharide, and its activity is highly regulated through phosphorylation at multiple sites and also by allosteric effectors, mainly glucose 6-phosphate (G6P) [].