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Nahrung. 2001 Oct;45(6):385-7.

Expression of legumin and vicilin genes in pea mutants and the production of legumin in transgenic plants.

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1
John Innes Centre, Norwich Research Park, GB-Norwich NR4 7UH, Great Britain. rod.casey@bbsrc.ac.UK

Abstract

Pea seeds contain two major storage proteins, legumin and vicilin, in proportions that are genetically and environmentally determined. They are synthesized from at least 40 genes and at least 10 different genetic loci. Mutant alleles at loci involved in starch synthesis, which result in perturbations in starch accumulation, also affect the expression of legumin genes, thereby influencing the legumin: vicilin ratio within the total seed protein. Examples of such alleles include r (starch-branching enzyme) and rb (ADP-glucose pyrophosphorylase), both of which result in a reduction in legumin synthesis; double mutants (rrb) show a particularly severe reduction in the amount of legumin. The effects of such mutations are specific to legumins. The amounts of vicilin are unaffected by mutations at r or rb. One of the consequences of the production of legumin from many genes is structural heterogeneity that is believed to preclude the purification of homogeneous legumin for crystallization and 3D-structure determination. Expression of cloned legumin cDNA in E. coli can result in sequence homogeneity, but E. coli is unable to carry out the normal proteolytic processing of legumin precursors and consequently such material is different from that produced in pea seeds. This paper describes the high-level synthesis, processing and assembly of pea legumin in transgenic wheat seeds, leading to the spontaneous in vitro formation of paracrystalline arrays of legumin, which may be attributed to the fact that the legumin consists of a single type of subunit. Such material might be used as a source of single-sequence, processed and assembled pea legumin for structural investigation.

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