The secondary structure of nucleic acids is probed by the psoralen photoreaction. Techniques have recently been developed in this laboratory for mapping such secondary structure. The objective of this proposal is to improve these techniques so that they can be used as a high resolution probe for secondary structure. When this objective is realized, the nucleotides in a defined sequence which are base-paired in a helical structure will be identifiable. The goals for the current year were: 1) A sequence resolution map of the hydroxymethyltrioxsalen (HMT) adducts and cross-links in Drosophila melanogaster 5S ribosomal RNA. 2) A sequence resolution map of hydroxymethyltrioxsalen adducts in E. coli phe tRNA. 3) The structure determination of all monoadducts of HMT formed in DNA utilizing mass spectrometry and high resolution NMR. 4) The dynamics of two-pulse laser excitation in promoting chemical cross-linkage of DNA.
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