Molecular characterization of a new arcelin-5 gene

Arcelins are insecticidal proteins found in some wild accessions of the com mon bean, Phaseolus vulgaris. They are grouped in six allelic variants and arcelin-5 is the variant with the highest inhibitory effect on the developm ent of Zabrotes subfasciatus larvae. Characterization of the protein and it s genes resulted in the identification of three polypeptides and the isolat ion of two genes that encode the Arc5a and Arc5b polypeptides. Here we desc ribe a new gene, Arc5-III. The protein it encodes has 81% amino acid identi ty with the derived amino acid sequences of Arc5-I and Arc5-II. The Arc5-II I gene is highly expressed in developing seeds and at a much lower level in roots. Data obtained by a combination of two-dimensional gel electrophores is, protein sequencing and MALDI-TOF mass spectrometry analysis support the conclusion that Arc5-III encodes a polypeptide present in Arc5c band, Usin g ion-exchange chromatography, three fractions containing arcelin-5 polypep tides were eluted by increasing the salt concentration. The three fractions contain various amounts of the three arc-5 polypeptides and inhibit the gr owth of Zabrotes subfasciatus larvae differentially, suggesting differences in insecticidal activity among the arcelin-5 isoforms. (C) 2000 Elsevier S cience B.V. All rights reserved.