ZEIN GENE ORGANIZATION IN MAIZE AND RELATED GRASSES
Abstract
The storage proteins of maize seed consist of a group of alcohol-soluble proteins called zein. Zein can be divided into 4 size classes by SDS-PAGE: 22,000, 19,000, 15,000 and 10,000 molecular weight. Those of the two larger classes can be further divided by 2-D gel electrophoresis. Clones of cDNAs made to zein mRNAs have shown the presence of several different mRNAs for each of the larger classes. Cloned sequences within a group are highly homologous with significant homology between groups. The results suggest a multigene family for the zein proteins. The clones have been used to study the organization of homologous zein genes within the maize genome. When individual clones of the two higher classes are used as probes for Southern blot hybridizations of genomic DNA, multiple restriction fragments are found to hybridize. At moderately stringent criteria, the hybridization patterns are complex; many restriction fragments show sufficient intensity to indicate clustering of zein sequences or co-migration of similarly sized fragments. At criteria permitting less cross-hybridization of homologous sequences (T(,m)-10(DEGREES)C), some bands are reduced in intensity or entirely eliminated. These results suggest the relative organization of the zein genes within a class. By controlling hybridization criteria, it should be possible to more readily distinguish particular zein genes in a Southern blot analysis. The Southern blot hybridization pattern for the 15,000 molecular weight zein is less complex. Only a single major band is found with sufficient intensity for 2-3 genes. All of the bands seen by hybridization with total zein cDNA can be accounted for by hybridization with individual cDNA clones. There does not, therefore, seem to be any bulk of sequences as yet undetected. Genomic Southern analyses of other maize inbreds and related grasses show similarly complex patterns with cDNA probes for the 19,000 and 22,000 molecular weight zeins, even at stringent criteria (T(,m)-20(DEGREES)C). This suggests an evolutionary conservation of these sequences. These results also suggest that gene duplication(s) giving rise to a zein multigene family occurred before divergence of the maize, teosinte, and Tripsacum species from a common ancestor.
Degree
Ph.D.
Subject Area
Genetics
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