A Magnesium Ion Core at the Heart of a Ribozyme Domain. Jamie H. Cate, Raven L. Hanna and Jennifer A. Doudna, Dept. of Molecular Biophysics and Biochemistry, Yale University.

Large ribozymes require divalent metal ions to fold. We show that the tertiary structure of the Tetrahymena group I intron P4-P6 domain nucleates around a magnesium ion core. In the domain crystal structure, five magnesium ions bind in a three-helix junction at the center of the molecule. Single atom changes that disrupt any one of four magnesium sites in this three-helix junction destroy folding of the entire 160-nucleotide P4-P6 domain. Thus a magnesium ion core drives packing in the P4-P6 domain and may provide a scaffold in the native structure of large RNAs in general, analogous to the hydrophobic core in proteins.