Zein, the prolamin of corn is a group of alcohol soluble proteins constituting about 50% of the total storage protein in maize endosperm. Zeins are resolved, in SDS-PAGE, mainly in four classes with apparent MW of 22, 20, 15 and 10 kDa. When analyzed by IEF, however, a complex protein-banding pattern is seen which is different for different inbred lines. Taking advantage of the large genetic variability existing among maize strains in the IEF and SDS polyacrylamide banding patterns of storage proteins, 20 structural loci, encoding for different zein polypeptides, have been mapped on chromosome 4 and 7 (H. Hartings et al., Genet. Agr. 38:447, 1985). Sequences of several zein genes have been identified and used as probes for the studies of their molecular organization. We have set up a strategy to associate zein polypeptides with specific DNA restriction fragments containing genes encoding for zein polypeptides. In this respect we have found, among several inbreds examined, that zein polypeptides designated Zp20/1, Zp20/2 and Zp20/3 are always simultaneously present or absent in different genotypes. The cluster of genes encoding for these polypeptides is on the short arm of chromosome 7, linked to the opaque-2 (o2) gene. The fact that we have never observed recombination within this cluster of genes suggested the possibility that they could be located on a single restriction DNA fragment.
In experiments involving segregation of the o2 gene with presence or absence of the three zein polypeptides, associated with the molecular analysis of the recombinant seeds, we detected that a restriction DNA fragment of 20 kb cosegregated with the presence of these polypeptides; this fragment was absent in DNA extracted from plants lacking the three zein polypeptides. This suggested that this fragment might contain the genes encoding one or even all three polypeptides.
R. Marotta, B. Vaciago, N. Di Fonzo, F. Salamini, C. Soave, M. Motto and A. Spada
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