Isolation and characterization of cDNAs encoding viscotoxins of mistletoe (VISCUM ALBUM)

Journal/Book: Eur. J. Biochem. 198 (3), 549-553. 1991;

Abstract: Viscotoxins have been isolated from leaf homogenates of Europeanmistletoe (Viscum album L.) and purified to apparent homogeneity.Antisera raised against these polypeptides were used to screen a cDNAexpression library in lambda gt11. Two positive clones have beenisolated, one encoding a full-length preprotein of viscotoxin A3 and theother encoding the precursor of viscotoxin B. Besides the viscotoxindomain the precursor contained a signal sequence and an acidicpolypeptide domain. Similar higher molecular mass precursor proteinshave been described for thionins of leaves and seeds of barley. Eventhough the acidic part of the viscotoxin precursor is much shorter thanthe corresponding domain of the precursors of the leaf and seed thioninsof barley, both the negative charge and the number and the relativeposition of cysteine residues have been conserved within the acidicdomain. This result is consistent with our proposal that the acidicdomain of the thionin precursor may play an important role in keepingthe thionin inactive within the plant cell. Author.

Keyword(s): AMINO-ACID-SEQUENCE

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