Chloride binding by the AML1/Runx1 transcription factor studied by NMR

It is known that the DNA binding Runt domain of the AML1/Runx1 transcriptio n factor coordinates Cl- ions. In this paper we have determined Cl- binding affinities of AML1 by Cl-35 nuclear magnetic resonance (NMR) linewidth ana lysis. The Punt domain binds Cl- with a dissociation constant (K-d,K-Cl) of 34 mM. If CBF beta is added to form a 1:1 complex, the K-d,K-Cl value incr eases to 56 mM. Homology modeling suggests that a high occupancy Cl- bindin g site overlaps with the DNA binding surface. NMR data show that DNA displa ces this Cl- ion. Possible biological roles of Cl- binding are discussed ba sed on these findings. (C) 2001 Federation of European Biochemical Societie s. Published by Elsevier Science B.V. All rights reserved.