title: Independent genetic control of maize starch-branching enzymes IIa and IIb. Isolation and characterization of a Sbe2a cDNA.
abstract: In maize (Zea mays L.) three isoforms of starch-branching enzyme (SBEI, SBEIIa, and SBEIIb) are involved in the synthesis of amylopectin, the branched component of starch. To isolate a cDNA encoding SBEIIa, degenerate oligonucleotides based on domains highly conserved in Sbe2 family members were used to amplify Sbe2-family cDNA from tissues lacking SBEIIb activity. The predicted amino acid sequence of Sbe2a cDNA matches the N-terminal sequence of SBEIIa protein purified from maize endosperm. The size of the mature protein deduced from the cDNA also matches that of SBEIIa. Features of the predicted protein are most similar to members of the SBEII family; however, it differs from maize SBEIIb in having a 49-amino acid N-terminal extension and a region of substantial sequence divergence. Sbe2a mRNA levels are 10-fold higher in embryonic than in endosperm tissue, and are much lower than Sbe2b in both tissues. Unlike Sbe2b, Sbe2a-hybridizing mRNA accumulates in leaf and other vegetative tissues, consistent with the known distribution of SBEIIa and SBEIIb activities.
authors.affiliation: Department of Horticulture, Pennsylvania State University, University Park 16802, USA.
authors.forename: M
authors.initials: M
authors.lastname: Gao
authors.forename: D K
authors.initials: DK
authors.lastname: Fisher
authors.forename: K N
authors.initials: KN
authors.lastname: Kim
authors.forename: J C
authors.initials: JC
authors.lastname: Shannon
authors.forename: M J
authors.initials: MJ
authors.lastname: Guiltinan
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007527:Isoenzymes / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014018:Tissue Distribution; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics*
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D018744:DNA, Plant; D007527:Isoenzymes; D012333:RNA, Messenger; D018749:RNA, Plant; D015061:1,4-alpha-Glucan Branching Enzyme