Stabilization of the tertiary structure of yeast phenylalanine tRNA by [Co(NH3)6]3+. X-ray evidence for hydrogen bonding to pairs of guanine bases in the major groove.

The sites of three [Co(NH3)6]3+ ions bound to the phenylalanine tRNA of yeast have been determined by X-ray diffraction analysis. [Co(NH3)6]3+ binds to purine-purine sequences in yeast tRNA Phe. It is different from the binding fo Co2+, which binds to the base and phosphate of residue G15. There are no direct metal-nucleotide bonds, although hydrogen bonding of the coordinated ammines to double-helical guanylguanosine sequences in the major groove and to phosphate oxygen in neighboring polynucleotide strands increases the stability of the structure. Hydrogen-bonding appears to be via cis ammine ligands to N(7) and O(6) positions of adjacent purine bases.