Cloning of cDNA and chromosomal location of genes encoding the three types of subunits of the wheat tetrameric inhibitor of insect alpha-amylase.

We have characterized three cDNA clones corresponding to proteins CM1, CM3 and CM16, which represent the three types of subunits of the wheat tetrameric inhibitor of insect alpha-amylases. The deduced amino acid sequences of the mature polypeptides are homologous to those of the dimeric and monomeric alpha-amylase inhibitors and of the trypsin inhibitors. The mature polypeptides are preceded by typical signal peptides. Southern blot analysis of appropriate aneuploids, using the cloned cDNAs as probes, has revealed the location of genes for subunits of the CM3 and of the CM16 type within a few kb of each other in chromosomes 4A, 4B and 4D, and those for the CM 1 type of subunit in chromosomes 7A, 7B and 7D. Known subunits of the tetrameric inhibitor corresponding to genes from the B and D genomes have been previously characterized. No proteins of this class have been found to be encoded by the A genome in hexaploid wheat (genomes AA, BB, DD) or in diploid wheats (AA) and no anti alpha-amylase activity has been detected in the latter, so that the A-genome genes must be either silent (pseudogenes) or expressed at a much lower level.