It is planned to continue our investigations on the binding of ligands to tRNA by using x-ray difference Fourier methods. Several metal and ligand binding studies have been successfully carried out in this laboratory and have led to some exciting and unexpected results such as: (i) the Pb2+ ion catalyzed cleavage of the tRNA chain has important implications in the processing of precursor tRNA to mature tRNA and in self splicing RNA; (ii) the unexpected binding of the peptide antibiotics netropsin and distamycin A in the major (deep) groove of the pseudouridine helix of tRNA in contrast to their preferred binding in the minor groove of DNA. These rsults are providing important insights into the molecular mechanism of drug interaction with nucleic acids. The interaction of other metal ions and ligands with tRNA are planned. (i) High concentration of Mg2+ and Eu3+ are known to cleave RNA. This reaction will be studied with tRNA crystals. (ii) Preliminary studies have indicated that Fe2+ and Fe3+ show different interaction properties with tRNA, the details of which will be investigated. (iii) The binding of actinomycin, daunamycin and streptomycin and other dyes and drugs to tRNA will be studied. (iv) It is planned to also study metal-phenanthroline complexes which are known to cut RNA and DNA (v) The antitumor agent titanocene dichloride has been shown to bind to tRNA crystals. The nature of this complex will be investigated. (vi) In addition to the studies on tRNA, it is planned to synthesize model oligoribonucleotides and investigate the interaction of various ligands with them. These studies will provide additional invaluable information on the nature and specific sites of interaction of various ligands with RNA and profoundly aid in the understanding of the molecular forces and mechanism of interaction of metals, drugs and other ligands with nucleic acids.
