THE PBC DOMAIN CONTAINS A MEINOX DOMAIN - COEVOLUTION OF HOX AND TALEHOMEOBOX GENES

A recent survey of TALE superclass homeobox genes revealed a new domai n upstream of the homeodomain that is conserved between the plant KNOX genes and the animal MEIS genes. At the same time, another paper iden tified the Drosophila gene homothorax (hth) as a homologue of the vert ebrate MEIS genes, which prompted a reexamination of the sequences of the MEIS, KNOX (collectively named MEINOX) and PBC domains. Similarity of the complete MEINOX domain was found within the PBC domain. This s uggests that the PBC class genes were also derived from the ancient ME INOX genes. Recently, it has been shown that the MEIS genes can intera ct with the Abd-B genes, whilst previous results have shown that the P BC genes interact with anterior Hox genes. This leads to the hypothesi s that the duplication of an ancestral MEINOX gene into the PBC and ME IS genes happened at a point in time when the first two Hox cluster ge nes, an anterior one and a posterior one, emerged, and that subsequent ly these gene classes coevolved.