Distinct HOX N-terminal Arm Residues Are Responsible for Specificity of DNA Recognition by HOX Monomers and HOX·PBX Heterodimers

doi:10.1074/jbc.272.13.8635

Distinct HOX N-terminal Arm Residues Are Responsible for Specificity of DNA Recognition by HOX Monomers and HOX·PBX Heterodimers*

From the ^‡ McGill Cancer Centre, and
Departments of ^§ Medicine (Division of Experimental Medicine) and
^∥ Oncology, McGill University, Montréal, Québec H3G 1Y6, Canada

** Chercheur-Boursier of the Fonds de la Recherche en Santé du Québec. To whom correspondence should be addressed:
McGill Cancer Centre, 3655 Drummond St., Montréal, Québec, Canada H3G 1Y6
. Tel.: 514-398-8937; Fax: 514-398-6769; E-mail: featherstone{at}medcor.mcgill.ca.

Abstract

Dimerization with extradenticle or PBX homeoproteins dramatically improves DNA binding by HOX transcription factors, indicating that recognition by such complexes is important for HOX specificity. For HOX monomeric binding, a major determinant of specificity is the flexible N-terminal arm. It makes base-specific contacts via the minor groove, including one to the 1st position of a 5′-TNAT-3′ core by a conserved arginine (Arg-5). Here we show that Arg-5 also contributes to the stability of HOX·PBX complexes, apparently by forming the same DNA contact. We further show that heterodimers of PBX with HOXA1 or HOXD4 proteins have different specificities at another position recognized by the N-terminal arm (the 2nd position in the TNAT core). Importantly, N-terminal arm residues 2 and 3, which distinguish the binding of HOXA1 and HOXD4 monomers, play no role in the specificity of their complexes with PBX. In addition, HOXD9 and HOXD10, which are capable of binding both TTAT and TAAT sites as monomers, can cooperate with PBX1A only on a TTAT site. These data suggest that some DNA contacts made by the N-terminal arm are altered by interaction with PBX.

Footnotes

↵^¶ Supported by a HydroQuébec/McGill Major Fellowship.
↵* This work was supported in part by grants (to M. S. F.) from the Medical Research Council of Canada and the National Cancer Institute of Canada. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

ARE

autoregulatory enhancer

EMSA

electrophoretic mobility shift assay.
↵² M. L. Phelan and M. S. Featherstone, unpublished results.
- Received December 11, 1996.
- Revision received January 16, 1997.