Molecular characterization of oat seed globulins

We have isolated full-length cDNA clones that encode oat (Avena sativa) seed storage globulin mRNAs from a cDNA library in the expression vector lambda gtll. The longest of these clones, pOG2, has an 1840-base pair insert that encodes a complete precursor subunit with a signal peptide of 24 amino acids followed by an acidic polypeptide of 293 amino acids and a basic polypeptide of 201 amino acids. Near the C terminus of the acidic polypeptide are four repeats of a highly conserved, glutamine-rich octapeptide. Other oat globulin cDNA clones contain five of these repeats. Nucleotide sequence comparisons between these clones indicate that the genes encoding these proteins are highly conserved. We estimate there to be 7 to 10 genes for the oat globulin per haploid genome. Comparisons of amino acid sequences show that the oat globulin is 30 to 40% homologous with storage globulins of legumes and about 70% homologous with the rice seed storage globulin (glutelin).     

A rice glutelin and a soybean glycinin have evolved from a common ancestral gene

A cDNA clone covering the entire coding region for a glutelin subunit precursor has been identified from a library of endosperm-developing rice cDNA clones using a mixed oligodeoxynucleotide probe, and then by immunoprecipitation of hybrid-selected translation product with an antiserum against the acidic polypeptides of the glutelin. Analysis of the cDNA insert revealed that rice glutelin is synthesized as precursor polypeptides which undergo post-translational processing to form the nonrandom polypeptide pairs, like glycinin precursors of soybean. By comparing the predicted protein sequence of this precursor from monocots with that of glycinin A1aB1b precursor from dicots, it was found that the overall 32% of the amino acid positions are identical in both proteins. Because regions which show identities are dispersed throughout both molecules, the similarity is not due to convergent evolution, but to divergence evolution from a common ancestral gene.     

Thioredoxin-catalyzed Refolding of Recombinant Protein: Refolding of Human Pro-urokinase

We have isolated four independent genomic DNA fragments encoding a rice storage protein, glutelin, by using its cDNA as a probe. Restriction mapping and sequencing analyses showed that all four clones encode type II mRNA of glutelin and have very similar nucleotide sequences. However, several differences were found among the four clones with respect to the nucleotide sequences of their coding and 5′-upstream regions, some of which confirmed corresponding changes in the amino acid sequences of the encoded proteins. These results indicate that the genes encoding type II mRNA species of glutelin constitute a multi-gene family of closely related members.     

Analysis of randomly isolated cDNAs from developing endosperm of rice (Oryza sativa L.): evaluation of expressed sequence tags,and expression levels of mRNAs

Using a cDNA library prepared from poly(A)⁺ RNA from 10-day-old rice endosperm, partial nucleotide sequences of randomly isolated clones were analyzed. A total of 153 (30.6%) out of 500 cDNA clones showed high amino acid identity to previously identified genes. There was significant redundancy in cDNAs encoding prolamine and glutelin. About 21.0% of the cDNA clones were found to code for seed storage protein genes. Consequently, 37 independent genes were identified. Using cDNA clones encoding glutelin, prolamine, seed allergen, -1,4-glucan branching enzyme, glycine-rich RNA binding protein, metallothionein, non-specific lipid-transfer protein and ubiquitin conjugating enzyme the accumulation of mRNA during rice seed development was compared. Genes associated with seed storage protein and starch biosynthesis were expressed according to expected developmental stages. Glycinerich RNA binding protein genes as well as metallothionein-like protein genes were highly expressed in developing seeds, but low in leaves of whole plants.     

Molecular cloning of a cysteine proteinase inhibitor of rice (oryzacystatin). Homology with animal cystatins and transient expression in the ripening process of rice seeds

A cDNA clone for a cysteine proteinase inhibitor of rice (oryzacystatin) was isolated from a lambda gt10 cDNA library of rice immature seeds by screening with synthesized oligonucleotide probes based on partial amino acid sequences of oryzacystatin. A nearly full-length cDNA clone was obtained which encoded 102-amino acid residues. The amino acid sequence of oryzacystatin deduced from the cDNA sequence was significantly homologous to those of mammalian cystatins, especially family 2 cystatins. Oryzacystatin contained the sequence Gln-Val-Val-Ala-Gly conserved among most members of the cystatin superfamily. The gene for oryzacystatin was transcribed into a single mRNA species of about 700 nucleotides. The content of mRNA reached its highest level 2 weeks after flowering and then gradually decreased to undetectable levels at 10 weeks. This feature of transient expression is coordinate with that of glutelin (a major storage protein), although the expression of oryzacystatin precedes that of glutelin by about 1 week.     

水稻谷蛋白是类似于豆球蛋白的蛋白质

水稻是我国的主要粮食作物,它的蛋白质含量为5—14%。在水稻种子蛋白质中,谷蛋白占80%,球蛋白占10%,醇溶蛋白占5%,清蛋白占5%。据报道,水稻种子清蛋白主要由分子量16800的亚基组成,球蛋白由10种不同分子量的亚基通过疏水交互作用相结合,谷蛋白由分子量38000、25000和16000三种亚基通过双硫键相结合:但是,Yamagata(1982)和作者(1983、1984、1986)的研究表明:水稻种子谷蛋白主要由分子量