Partial amino acid sequence from hordein polypeptide B1

Molecular biology of the grain storage proteins of the Triticeae

Chemical studies show that there are close relationships between the storage proteins of the Triticeae. We have investigated these relationships by the study of the synthesis of the proteins in vivo and in vitro , and by making libraries of double-stranded complementary DNA (cDNA) derived from poly A + RNA isolated from developing endosperms of barley, wheat and rye. These cDNA clones have been used to probe the organization and regulation of expression of the Hor loci in barley. The results suggest that regulation of synthesis is generally achieved by changes in the amounts of mRNA for the different proteins, both in response to time of development and the relative supply of sulphur and nitrogen, although there may also be differences in the relative amounts of mRNA translated. The sequencing of the cDNA clones has shown the im portance of repeated sequences in the evolution of prolamin genes.

The structural and evolutionary relationships of the prolamin storage proteins of barley, rye and wheat

The major endosperm storage proteins of barley, wheat and rye are soluble in aqueous alcohols, either native or after the reduction of disulphide bonds, and can be defined as prolamins. They can be divided into three groups on the basis of their chemical characteristics, notably their molecular mass and amino acid composition, and the chromosomal location of their structural genes. Two of the groups, the high molecular mass prolamins and the sulphur-poor (ω-gliadin-type) prolamins, show clear homology between the three species. The remaining prolamins are characterized by a high content of cysteine. In wheat this is a complex mixture of at least three groups of components that vary in their aggregation properties and N-terminal amino acid sequences. The precise chemical and genetic relationships of those components to each other and to the more clearly defined groups of sulphur-rich prolamins of rye and barley are still not completely understood.

Secondary structure prediction of seed storage proteins

The comparison of partial primary structure of seed storage proteins leads to show homologies inside of each considered family (Legume seed legumins and cereal prolamins). Predicted secondary structures deduced from the presently known sequences also exhibit considerable homologies, which implies a severe conservatism of these proteins. Short repetitive segments of sequence of 5-20 residues are frequently occurring and give rise to the prediction either of beta-structure (or alpha-helix) bonded by beta-turns or of successive beta-turns. The latter conformation, which would be able to form a helicoidal arrangement, could contribute to a maximal packing of the protein molecules inside of the subcellular organelles (protein bodies) within which they are confined. As the only known function of seed storage proteins is to provide amino acids to the embryo, it is suggested that their ability to occupy a minimal volume is actually a reasonable explanation of their extreme conservatism in the course of evolution.

Molecular analysis of a mutation conferring the high-lysine phenotype on the grain of barley (Hordeum vulgare)

We have analyzed the molecular nature of the Riso 56 mutation that occurs in barley. This mutation results in a depression of hordein accumulation in the grain and consequently in a higher overall lysine content. In particular, the amount of B hordein, which is encoded by the complex locus Hor-2, is decreased by about 75% because of the absence of the major components. The synthesis of certain minor polypeptides, with properties similar to the major B hordeins, remains unaffected. Analysis of endosperm RNA, by in vitro translation and hybridization to various cloned cDNAs derived from hordein mRNA, shows that mRNA for the major B hordeins is not present in the endosperm. Hybridization of a B hordein cDNA clone to gel-fractionated restriction digests of mutant and wild-type DNA indicates that at least 85 kb of DNA has been deleted from the Hor-2 locus in the high-lysine mutant.

Mapping of the Hor-3 locus encoding D hordein in Barley

The hordein storage proteins of barley (Hordeum vulgare L.) are of intense interest due to their genetic diversity and prominence and impact on the industrial and agricultural uses of the seed. Two major hordein loci have been previously mapped on chromosome 5 (Hor-1 and Hor-2 encoding the C and B hordeins, respectively). A third major locus, Hor-3, which codes for D hordein, has been located in the centromeric region of chromosome 5, probably on the long arm. Two allelic variants with apparent molecular weights of 83,000 and 91,000 and similar isoelectric points of 8.0 comprise the products of this locus in the barley varieties 'Advance' and 'Triple Awned Lemma'. The D hordein examined is similar in molecular weight and isoelectric point to the high molecular weight (HMW) glutenin proteins encoded by the 1B chromosome of wheat (Triticum aestivum L.).

Cereal prolamin evolution and homology revealed by sequence analysis

Prolamin mixtures were isolated from oats, rice, normal and high-lysine sorghum, two varieties of pearl millet, two strains of teosinte, and gamma grass and subjected to NH2-terminal amino acid sequence determinations. In each case (except for rice, whose prolamins apparently have blocked or unavailable NH2-terminal residues), primarily a single sequence was observed despite significant heterogeneity, suggesting that prolamin homology in each cereal arose through duplication and mutation of a single ancestral gene. Comparisons were then made to prolamin sequences previously determined for wheat, corn, barley, and rye. Within genera, different varieties or subspecies exhibited few differences, but more distantly related genera, subtribes, and tribes showed increasingly large differences. Within the subfamily Festucoideae, no homology was apparent between prolamins of oats and those of the subtribe Triticinae (including wheat, rye, and barley, for which prolamin homology was previously demonstrated). Within the subfamily Panicoideae, corn was shown to be closely related to teosinte but more distantly to Tripsacum. Sorghum was shown to have diverged less from corn than had millet. These comparisons demonstrate that prolamin sequence analyses can successfully predict and clarify evolutionary relationships of cereals.