On the chemistry of RNA degradation by Fe-bleomycin

The chemistry of RNA degradation by Fe bleomycin was studied using two RNA substrates that are modified efficiently at a small number of sites by the antitumor antibiotic. Cleavage of a tRNA(His) precursor transcript by Fe(II).BLM A(2) was shown to require O-2; cleavage was also observed when the same substrate was treated with Fe(III).BLM A(2) + H2O2. Consistent with earlier observations made for DNA, the extent of tRNA(His) precursor cleavage was greater for Fe(II).BLM A(5), than for Fe(II).BLM A(2); the least cleavage was obtained using Fe(II).BLM demethyl A(2). By the use of a P-32 end labeled tRNA precursor transcript that was also H-3 labeled within the uracil moieties, it was shown that release of uracil was nearly stoichiometric with tRNA strand scission by Fe(II).BLM A(2). Nonetheless, treatment of the tRNA(His) with hydrazine following BLM-mediated cleavage indicated formation of a new product that must have derived from a BLM-induced lesion. Also employed far characterization of BLM cleavage of RNA were the octanucleotides CGCTAGCG, C-3-ribo-CGCTAGCG and C-3-ara-CGCTAGCG. Analysis of the products of cleavage indicates that Fe . BLM is capable of mediating cleavage by abstraction of a H atom either from C-4'H or C-1'H of the chimeric oligonucleotides. (C) 1997 Elsevier Science Ltd.