CLONING OF RAT HOMEOBOX GENES

We report the isolation of nine rat cognates of mouse homeoboxes withi n the four Hox gene clusters and a rat homologue of mouse IPF1 homeobo x, RHbox#13A. The sequences of nine cloned homeoboxes are highly simil ar to those of the mouse and human homeoboxes in the Hox clusters. The restriction enzyme sites and map distances between each of the homeob oxes on the rat genome are nearly identical to those of mouse and huma n Thus, we conclude that the isolated homeoboxes are the rat homologue s of mouse homeoboxes within the four Hox clusters. A novel homeobox R Hbox#13A is different from the Drosophila Antennapedia (Antp) sequence but is highly similar to the XlHbox8 (Xenopus laevis) and HtrA2 (Helo bdella triserialis) homeoboxes. Forty-two amino acids of the last two- thirds of the RHbox#13A, XlHbox8, and mouse IPF1 homeodomains complete ly matched. in addition, these four homeodomains contain a unique His residue in the recognition. helix of a helix-turn-helix DNA-binding mo tif. This His residue is not found in any of the previously published mammalian homeodomain sequences except mouse IPF1.