Highly clustered zein gene sequences reveal evolutionary history of the multigene family

We have determined the nucleotide sequences of zein cDNA clones ZG14, ZG15, and ZG35. The three clones have 95 to 98% homology to the previously published sequence of clone A20, and 84% homology to sequences of the zein subfamily A30. Comparison of all sequences of the A30 and A20 subfamilies highlights the following features: the 5' nontranslated regions are 68 and 57 nucleotides in length for the A20- and A30-like mRNAs, respectively, and contain at least three repeats of the consensus sequence ACGAACAAta/gG; the majority of these genes are highly clustered as judged from pulsed-field gel electrophoresis of high molecular weight maize DNA. Furthermore, we discuss a model for the evolution of the multigene family which stresses the special importance of unequal crossingover and gene conversion in this system.