We report the isolation of nine rat cognates of mouse homeoboxes within the fourHox gene clusters and a rat homologue of mouseIPF1 homeobox,RHbox# 13A. The sequences of nine cloned homeoboxes are highly similar to those of the mouse and human homeoboxes in the Hox clusters. The restriction enzyme sites and map distances between each of the homeoboxes on the rat genome are nearly identical to those of mouse and human. Thus, we conclude that the isolated homeoboxes are the rat homologues of mouse homeoboxes within the four Hox clusters. A novel homeoboxRHbox# 13A is different from theDrosophila Antennapedia (Antp) sequence but is highly similar to theXlHbox8 (Xenopus laevis) andHtrA2 (Helobdella triserialis) homeoboxes. Forty-two amino acids of the last two-thirds of theRHbox# 13A, XlHbox8, and mouseIPF1 homeodomains completely matched. In addition, these four homeodomains contain a unique His residue in the recognition helix of a helix-turn-helix DNA-binding motif. This His residue is not found in any of the previously published mammalian homeodomain sequences except mouseIPF1.
Key wordsratHox cluster rat homologue of mouseIPF1 Rhbox# 13A XlHbox8 HtrA2
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