Genomic organization of an alpha-zein gene cluster in maize.

The genes encoding the alpha-zein proteins of maize constitute a large multigene family of some 75 genes. This multigene family can be divided into four subfamilies based on the nucleotide sequences of their genes and the deduced amino acid sequences of their proteins. We describe for the first time evidence of a clustering of five alpha-zein subfamily 4 (SF4) genes that are members of one of the major alpha-zein subfamilies in a 56 kb region of the genome of the maize inbred line W22. None of the other three known alpha-zein gene subfamilies (SF1, SF2, or SF3) are present in this cluster. The genomic region was reconstructed using restriction endonuclease maps to identify and align three overlapping cosmid clones isolated from a genomic library. The alpha-zein genes are not evenly spaced; the minimum distance between genes is 3.5 kb; the maximum is 13 kb. All the alpha-zein genes in the cluster have the same transcriptional orientation. The location and sequences of some of the repetitive DNA elements in this gene cluster were determined. We estimate that there are a minimum of eight repetitive DNA elements in this region. The sequences of the repetitive elements (not functionally defined) are located between or among the alpha-zein genes. The regions containing two of these repetitive elements (Rep1 and Rep4) have been sequenced; they are about 15 kb apart in the genome. These repetitive elements have similar sequences for about 300 bp out of the 400 bp compared. The regions of sequence similarity, however, are in reverse orientation to one another.(ABSTRACT TRUNCATED AT 250 WORDS)