AtMSI4 and RbAp48 WD-40 repeat proteins bind metal ions

The mammalian RbAp48 protein is the most extensively studied member of the conserved family of Msi1-like WD-40 repeat proteins, which are components o f complexes involved in the assembly and modification of chromatin, We have isolated a plant homolog of RbAp48, AtMSI4, By metal affinity chromatograp hy, zinc blotting and atomic absorption analysis, we demonstrate that purif ied recombinant RbAp48 and AtMSI4 proteins bind 3-4 metal ions per molecule of protein. Metal competition assays indicate a preference for zinc. Both N- and C-terminal halves of RbAp48 and AtMSI4 display zinc binding activity , suggesting it is an intrinsic property of the propeller structures likely to be formed by these proteins. Metal binding might mediate and/or regulat e protein-protein interactions which are functionally important in chromati n metabolism, (C) 1998 Federation of European Biochemical Societies.