Molecular structure of 1-methyl-4-thiouracil-9-methyladenine: unusual base pair in tRNA.

Abstract

4-THIOURIDINE is a constituent of the tRNA of Escherichia coli1–3. It is located in a position where, according to the cloverleaf model, specific base pairing by hydrogen bonding is assumed not to occur. X-ray crystallographic4 and spectral analyses5 of the monomer and polymer nucleoside have been performed and 4-thiouridine is the first pyrimidine nucleoside that has been shown to exist in a syn conformation in the crystalline state. We now report studies on the molecular structure of the l-methyl-4-thiouracil.9-methyladenine complex.