CLONING AND CHARACTERIZATION OF SEVERAL CDNAS FOR UDP-GLUCOSE PYROPHOSPHORYLASE FROM BARLEY (HORDEUM-VULGARE) TISSUES

Eleven cDNA clones encoding UDP-glucose pyrophosphorylase (UGPase) hav e been isolated from cDNA libraries prepared from seed embryo, seed en dosperm and leaves of barley (Hordeum vulgare L.). The sequences were identical, with the exception of positioning of the poly(A) tail; at l east five clones with different polyadenylation sites were found. For a putative full-length cDNA [1775 nucleotides (nt) plus polyadenylatio n tail], isolated from an embryo cDNA library, an open reading frame o f 1419 nt encodes a protein of 473 amino acids (aa) of 51.6 kDa. An al ignment of the derived aa sequence with other UGPases has revealed hig h identity to UGPases from eukaryotic tissues, but not from bacteria. Within the aa sequence, no homology was found to a UDP-glucose-binding motif that has been postulated for a family of glucosyl transferases. The derived aa sequence of UGPase contains three putative N-glycosyla tion sites and has a highly conserved positioning of five Lys residues , previously shown to be critical for catalysis and substrate binding of potato tuber UGPase. A possible role for N-glycosylation in the int racellular targeting of UGPase is discussed.