SPECIFIC RNA CLEAVAGES INDUCED BY MANGANESE IONS

The specificity and efficiency of manganese ion-induced RNA hydrolysis was studied with several tRNA molecules, In case of yeast tRNA(Phe), the main cleavage occurs at p16 and minor cuts at p17-18, p20-21, p34 and p36-37. The major Mn(Il)-induced cut in yeast elongator tRNA(Met) is also located in the D-loop at p16 and it is stronger than that obse rved in tRNA(Phe). In initiator tRNA(Met) from yeast two strong Mn(II) cleavages of equal intensity occur at p16 and p17. This is in contras t with single, much weaker cuts induced in the D-loop of that tRNA by Mg(II), Eu(III) and Pb(II) ions. Interestingly in case of yeast tRNA(G lu) the main cleavage caused by Mn(II), Mg(II) and Pb(II) ions occurs in the anticodon loop. The involvement of hypermodified base mnm(5)S(2 )U in this cleavage was ruled out based on results obtained,vith in vi tro transcript of yeast tRNA(Glu) anticodon arm, Mutation of a single base A37G in the anticodon loop of the transcript drastically reduced the specificity of Mn(II)-induced hydrolysis.