MOLECULAR ANALYSIS OF WILD-TYPE AND MUTANT ALLELES AT THE OPAQUE-2 REGULATORY LOCUS OF MAIZE REVEALS DIFFERENT MUTATIONS AND TYPES OF O2 PRODUCTS

The expression of the various members of the zein multigene family in maize endosperm is controlled by different regulatory loci. One of these loci, Opaque-2, coding for a bZIP transcriptional factor, controls the expression of a subset of zein genes. Analysis of genomic DNA from plants carrying wild-type (02) or mutant 02 alleles shows specific DNA restriction patterns that correlate with transcript types and their various gene products. Northern and western analyses show the presence in different wild types of a 1.7 kb transcript coding for different sizes of normal 02 proteins that migrate as doublets in the 68-72 kDa range. Among the various 02 mutants analysed we showed the occurrence of various null-transcript alleles, the presence of alleles with a normal size transcript which, however, produce a different-sized 02 protein, and a mutant producing both a normal size transcript and a longer transcript, but generating only a single 02 product migrating around 40 kDa. Analysis of other mutations (o7, fl2) known to affect zein polypeptide synthesis shows no interference of these mutations in the expression of the 02 gene products. The overall results indicate the occurrence of micro heterogeneity in the 02 wild-type genes and a broad spectrum of 02 mutations, both producing different sizes of 02 or 02 proteins. A nomenclature of the 02 and 02 genes based on the RFLP, transcripts and products of the various alleles is presented.