Analysis of Complementary and Genomic DNA Coding for a Highly Abundant Class of mRNA in Developing Field Bean Seeds (Vicia faba L. var. minor cv. Fribo)

Localization of seed protein genes on metaphase chromosomes of Vicia faba via fluorescence in situ hybridization

Using fluorescence in situ hybridization (FISH), four different seed protein genes were physically mapped on metaphase chromosomes of Vicia faba L. dropped on slides. FISH with a 2.8 kb genomic probe of a legumin B4 gene resulted in reproducible signals on the long arm of chromosome III near the centromere. The same clone cross-hybridized at a lower frequency to the short arm of chromosome II, where the closely related legumin B3 gene family is located. The locus for legumin A-genes could be detected in the distal half of the long arm of chromosome V using a 1.7 kb cDNA clone. The locus of an unknown seed protein gene was mapped to the long arm of chromosome I using a mixture of polymerase chain reaction-amplified DNA fragments of the coding region of up to 1 kb in size.

Abundant embryonic mRNA in field bean (Vicia faba L.) codes for a new class of seed proteins: cDNA cloning and characterization of the primary translation product

cDNA clones have been constructed bearing inserts for a specific mRNA class of high abundance in developing seeds of field bean (Vicia faba L.). Three full-length clones representing transcripts of different genes were sequenced and conceptually translated into a M=30 000 primary gene product. The structural analysis of the derived amino acid sequence revealed distinct domains: (i) a cleavable signal peptide; (ii) a hydrophilic N-terminal stretch possessing two serine clusters; (iii) a valine cluster and a hydrophobic domain in the C-terminal part of the polypeptide. The amino acid sequence of the polypeptide does not show homology with other known proteins.The corresponding mRNA could be isolated using cDNA clones and was efficiently translated in various systems. In a cell-free system the presence of a functional signal peptide was shown, which interacts with the signal recognition particle resulting in a cotranslational translocation across the membrane of the endoplasmic reticulum. If synthesized in Xenopus oocytes the translation product of the mRNA was secreted out of the cell. Homologous mRNA was found to be present also in developing cotyledons of pea (Pisum sativum L.) and french bean (Phaseolus vulgaris L.).