A rapid cytosine-specific modification of E. coli tRNA Leu 1 by semicarbazide-bisulfite, a probe for polynucleotide conformations.

Cytosine residues in 32P-labeled E. coli tRNA Leu 1 were modified by treatment of the tRNA with the semicarbazide-bisulfite reagents [Hayatsu, H. (1976) Biochemistry 15, 2677-2682]. Analysis of the modification sites showed that only four cytidine residues, i.e. C35, C53, C85 and C86, reacted. They were identical with the cytidines of this tRNA accessible to methoxyamine [Chang, S. E. and Ish-Horowicz, D. (1974) J. Mol. Biol. 84, 375-388] and the accessibility was consistent with the conformational features recognized for tRNA in general. The rapidity and the simple nature of this modification demonstrate that the semicarbazide-bisulfite reaction is a useful tool in studying conformations of polynucleotides.