[Structural organization of C-hordein genes from barley]

Three nucleotide sequences from the barley genome, containing the C-hordein genes lambda CH1, lambda CH3, and lambda CH5, were cloned. They were shown to have different physical maps, and the structural organization of homologous sequences was found to be highly conservative. The surrounding sequences of C-hordein genes contain insertions specific in length and copy number. A Hind III fragment of about 3000 bp in size of the lambda CH5 clone contains a highly repeated nucleotide sequence. The lambda CH3 clone contains two "head-to-head" repeated C-hordein genes. This is the first evidence that hordein genes may be located in the immediate vicinity of each other in a 17,800-bp region. A 919-bp nucleotide sequence of one of the C-hordein genes from this clone, pCHOR3, was determined. An open reading frame of 363 bp codes for a potential polypeptide consisting of 121 amino acids. The main part of the mature polypeptide consists of repeated octapeptide Pro-Gln-Gln-Pro-Phe-Pro-Gln-Gln motifs. The coding region has no introns. The 5' untranslated region contains regulatory loci specific for prolamin genes: the -300 element and the CAAT, AGGA, and TATA boxes. Significant differences in the lengths of the coding regions of cloned genes were observed: 363 and 1000 bp in the lambda CH3 clone, 500 bp in the lambda CH1 clone, and 600 bp in the lambda CH5 clone, which may be a molecular cause of C-hordein size polymorphism.