NARBONIN, A NOVEL 2S PROTEIN FROM VICIA-NARBONENSIS L SEEDS - CDNA, GENE STRUCTURE AND DEVELOPMENTALLY-REGULATED FORMATION

cDNA and genomic clones encoding narbonin, a 2S globulin from the seed of narbon bean (Vicia narbonensis L.), were obtained using the polyme rase chain reaction (PCR) and sequenced. The full-length cDNA as well as genomic clones contain a single open reading frame (ORF) of 873 bp that encodes a protein with 291 amino acids comprising the mature narb onin polypeptide (M(r) ca. 33 100) and an initiation methionine. The d educed amino acid sequence lacks a transient N-terminal signal peptide . The genomic clones do not contain any intron. No homology was found to nucleic acid and protein sequences so far registered in sequence da ta libraries. The biosynthesis of narbonin during embryogenesis is dev elopmentally-regulated and its pattern of synthesis closely resembles that of typical seed storage globulins. However, during seed germinati on narbonin was degraded very slowly, indicating that it may have othe r function than storage protein. Southern analysis suggests the existe nce of a small narbonin gene family. Narbonin genes were also found in four different species of the genus Vicia as well as in other legumes such as Canavalia ensiformis and Glycine max. In Escherichia coli a r ecombinant narbonin was produced which yielded crystals like those pre pared from narbonin purified from seeds.