Single nucleotide modulation of uridine to pseudouridine rearrangement in transfer RNA catalyzed by pseudouridine...

E. coli pseudouridine synthase I (PSUI) catalyzes the rearrangement of uridine residues in positions 38, 39 and 40 of tRNA transcripts to pseudouridine. These positions are located in the anticodon stem-loop of the tRNA molecule. Fourteen different E. coli tRNAs are substrates for the enzyme, whereas four other tRNAs which contain uridine in position 38 are not. Investigations were focused on the basis of enzyme differentiation between substrate and non-substrate tRNAs. Comparison of modification reactions with mutant and wild-type tRNA transcripts demonstrates that the presence of a G36 residue modulates modification by PSUI at position 38. In addition to local sequence effects, steady-state kinetic analyses suggest the existence of other recognition elements distinct from the immediate vicinity of modification.