Molecular cloning of rat liver glycogen synthase

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Biochemistry and Molecular Biology

First Committee Member

Ernest Y. C. Lee, Committee Chair


The cDNA for rat liver glycogen synthase was isolated by screening a rat liver cDNA library constructed in $\lambda$gt11. The cDNA was 2.4 kb in length and encoded a protein of 703 amino acid residues with a molecular mass of 80.5 kDa. Comparison of the rat liver and the human muscle sequences show that the N-terminal and C-terminal regions are quite divergent as compared to the internal sequences which show an 80% identity. The rat liver C-terminal region is truncated by 33 residues and has only 46% identity with the muscle sequence but retains the common feature of a low content of hydrophobic amino acids (13%). Phosphorylation sites 1a and 1b, which are the primary targets for phosphorylation by cAMP-dependent protein kinase, are absent in the liver sequence. The presence of these divergent, structurally anomalous C-terminal regions in liver and muscle glycogen synthase suggests the absence of the requirement that they possess a tertiary structure that is integral to that of the protein core. A model is proposed in which this region interacts with a catalytic core to maintain the I state, and in which phosphorylation serves to uncouple this interaction.


Biology, Molecular

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