Characterization of Polypeptides Corresponding to Clones of Maize Zein mRNAS

Zeins, the storage proteins of maize (Zea mays) are a complex group of polypeptides encoded by a large multigene family. The alpha-zein proteins, which account for about 70% of the total, show both size and charge heterogeneity. Although clones corresponding to several different alpha zeins have been characterized, it has not been possible to correlate these sequences with individual zein polypeptides. By translating in Xenopus oocytes RNAs transcribed in vitro from cloned zein mRNAs, we were able to identify the encoded proteins among native zeins or zeins synthesized in oocytes with total zein mRNA. There was no correlation between the isoelectric points of these proteins and the homology of their coding DNA sequences, as the proteins encoded by two closely homologous cDNAs migrated with greater charge heterogeneity than those encoded by less homologous clones. In addition, the size of the proteins as determined by SDS polyacrylamide gel electrophoresis did not always correlate with the length of the protein deduced from the DNA sequence. The ability to match cloned zein sequences to individual native proteins will enable the genetic mapping of cloned genes as well as the analysis of their translational regulation.