Sequence, regulation, and evolution of the maize 22-kD alpha zein in gene family

We have isolated and sequenced all 23 members of the 22-kD alpha zein (zlC) gene family of maize. This is one of the largest plant gene families that has been sequenced from a single genetic back.-round and includes the large st contiguous genomic DNA from maize with 346,292 bp to date. Twenty-two of the zlC members are found in a roughly tandem array on chromosome 4S Formi ng a dense gene cluster 168,489-bp long. The twenty-third copy of the gene family is also located on chromosome 4S at a site similar to 20 cM closer t o the centromere and appears to be the wild-type allele of the floury-2 (fl 2) mutation. On the basis of an analysis of maize cDNA databases, only seve n of these genes appear to be expressed including the fl2 allele. The expre ssed genes in the cluster are interspersed with nonexpressed genes. Interes tingly, some of the expressed genes differ in their transcriptional regulat ion. Gene amplification appears to be in blocks of genes explaining the rap id and compact expansion of the cluster during the evolution of maize.