The complete amino acid sequence for an atype gliadin protein of wheat (Triticum aestivum Linnaeus) endosperm has been derived from a cloned cDNA sequence. An additional cDNA clone that corresponds to about 75% of a similar a-type gliadin has been sequenced and shows some important differences. About 97% of the composite sequence of A-gliadin (an a-type gliadin fraction) has also been obtained by direct amino acid sequencing. This sequence shows a high degree of similarity with amino acid sequences derived from both cDNA clones and is virtually identical to one of them. On the basis of sequence information, after loss of the signal sequence, the mature a-type gliadins may be divided into five different domains, two of which may have evolved from an ancestral gliadin gene, whereas the remaining three contain repeating sequences that may have developed independently.The gliadins constitute a major fraction of the storage proteins of hexaploid (6x, AABBDD) wheat grain (Triticum aestivum Linnaeus) (1). They are important dietary proteins and determinants of dough and bread-baking quality but are limited in nutritional quality by low levels of lysine (1,2). In addition, gliadins, or peptides derived from them during digestion, initiate damage to the absorptive epithelium of the small intestine to produce the consequent symptoms of celiac disease in susceptible individuals (3, 4).Gliadins, which are synthesized on membrane-bound ribosomes in the endosperm cells during grain development (5,6), are separated into 35-50 components by two-dimensional electrophoresis (7,8); all components are rich in glutamine (30-50 mol %) and proline (15-30 mol %). On the basis of NH2-terminal amino acid sequences, gliadins may be grouped into three subfamilies (9, 10), a-type, -type, and wtype. Corresponding gene subfamilies are located on the short arms of homoeologous-group-1 chromosomes for y type and cw-type gliadins or on the short arm of group-6 chromosomes for a-type gliadins (11).We report here the primary sequences of a-type gliadins determined by DNA sequencing of complementary DNA (cDNA) clones and by amino acid sequencing of A-gliadin (an aggregable type of a-gliadin) (1). The a-type gliadins possess a unique protein structure that includes a signal sequence (absent from the mature proteins) plus five peptide domains, each having a distinctive amino acid composition. MATERIALS AND METHODSConstruction of a Wheat cDNA Library. Poly(A)+ RNA from developing wheat grain of the cultivar 'Cheyenne' was prepared and fractionated as described by Okita and Greene (6). Double-stranded cDNA was prepared by a modification (12) of the method of Wickens et al. (13) and inserted into the unique Pst I site of pBR322 by oligo(dG)-oligo(dC) tailing (14). The recombined cDNA plasmids were then used to transform Escherichia coli RR1.Identification of a-Type Gliadin cDNA Plasmids. Colony hybridization (15) was performed with 32P-labeled, reversetranscribed wheat endosperm poly(A)+ RNA. Hybrid-selected translation and NaDodSO4/polyacrylami...

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