 Pseudouridine exerts a subtle but significant influence on the nearby sugar-phosphate backbone and also enhances base stacking.These effects may underlie the biological role of most, but perhaps not all of the pseudouridine residues in RNA.Certain genetic mutants lacking specific pseudouridine residues in tRNA or rRNA exhibit difficulties in translation, display slow growth rates, and fail to compete effectively with wild-type strains in mixed culture.