A novel multigene family that the gene for a maize DNA-binding protein, MNB1a belongs to: isolation of genomic clones from this family and some aspects of its molecular evolution

Abstract

MNB1a is a DNA-binding protein of maize that contains a unique DNA-binding domain, designated the Dof domain, and its gene belongs to a multigene family. In putative proteins encoded by cDNA clones of the multigene family, the Dof domain was strongly conserved. In this study, two maize genomic clones of this multigene family were isolated. Although these clones did not contain the MNB1a gene, RNA transcripts corresponding to genomic clones were detected, suggesting that the clones encode authentic proteins. These clones contained sequences homologous to a portion of the sequence of the MNB1a cDNA. Unexpectedly, however, this region did not correspond to the Dof domain but to a region just downstream of the Dof domain. Although these observations seemed to suggest that the MNB1a gene family might have evolved via recombination between a DNA-binding domain and other functional domains, the MNB1a gene seemed to have no introns in the coding region. These results suggest that a simple exon-shuffling model is not sufficient to explain the molecular evolution of this multigene gene family but that complicated recombination played an important role in the evolution.