Taxonomic distribution of proteins containing HALZ domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing HALZ domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Structure of homeobox-leucine zipper genes suggests a model for the evolution of gene families.

Schena M, Davis RW
Proc Natl Acad Sci U S A. 1994; 91: 8393-7

Homeobox genes are present in both plants and animals. Homeobox-leucine zipper genes, however, have been identified thus far only in the small mustard plant Arabidopsis thaliana. This observation suggests that homeobox-leucine zipper genes evolved after the divergence of plants and animals, perhaps to mediate specific regulatory events. To better understand this gene family, we isolated several sequences containing the homeobox-leucine zipper motif and carried out a comparative analysis of nine homeobox-leucine zipper genes (HAT1, HAT2, HAT3, HAT4, HAT5, HAT7, HAT9, HAT14, and HAT22). Gene structures, sequence comparisons, and chromosomal locations suggest a simple model for the evolution of these genes. The model postulates that a primordial homeobox gene acquired a leucine zipper by exon capture. The nascent homeobox-leucine zipper gene then appears to have undergone a series of gene duplication and chromosomal translocation events, leading to the formation of the HAT gene family. This work has general implications for the evolution of regulatory genes.