The molecular mechanisms regulating the accumulationof the major maize storage proteins, zeins, have been investigated with a view to improving the nutritional value of maize kernels. Strategies have been proposed for the molecular cloning of 2 high lysine mutants (opaque-2 and opaque-6). These genes may possess regulatory functions used in different combinations: the O2 locus affects O6 which is reported to control positively the synthesis of 20 and 22 kDa zein proteins. However, by itself, O2 only acts positively on the 22 kDa class. The study of these genes may prove decisive in understanding the role of the O2 and O6 loci in regulating the deposition of zein.

The complementary deoxyribonucleic acid (cDNA) and genomic sequences coding for the b-32 protein, an albumin expressed in maize endosperm cells under the control of O2 and O6 loci were cloned and the complete amino acid sequence of the protein derived. The structure of the b-32 protein, a putative regulatory factor of zein expression, has a central acid region separated by 2 domains covered by secondary structure motifs. Genetic analysis suggested that the O2 locus in maize acts as a positive transacting, transcriptional activator of the zein gene expression. This regulatory locus was successfully cloned through transposon tagging. The structure of this locus was determined by sequence analysis of genomic and cDNA clones. The O2 protein contains a domain similar to the leucine zipper motif identified in deoxyribonucleic acid (DNA) binding proteins of animal protoocogenes and in transcriptional activators. In conclusion, these studies led to an understanding of the mechanisms controlling zein gene expression, which may prove useful for practical application of genetic engineering of these seed proteins.