The single pseudouridine residue in Escherichia coli 16S RNA is located at position 516.

Received June 29, 1994; Accepted July 27, 1994ABSTRACTThe number and location of pseudouridine residues inEscherichia coli 16S ribosomal RNA has beendetermined by a combination of direct and indirectmethods. Only one residue was found, at position 516.This site is at the 5'-end of one of the three most highlyconserved long sequences of this RNA molecule. Anumber of experimental findings have stronglyimplicated this loop in the fidelity of codon recognitionby A-site bound tRNA. By virtue of its location, wesuggest that *516 may also play a role in maintainingthe fidelity of protein synthesis.INTRODUCTIONThe dominant role of RNA in ribosome function is now wellestablished (reviewed in 1—3). Less well appreciated is the factthat rRNA contains a number of modified nucleosides (4) whosespecificity of placement strongly implies that they play apurposeful role. These are nucleosides methylated either on thebase or on the 2'-hydroxyl of ribose and pseudouridine (¥, 5-/3-D-ribofuranosyluracil), the 5-ribosyl isomer of uridine, and itsderivatives, such as l-methyl-3-(3-amino-3-carboxypropyl)pseudouridine in eukaryotic small subunit rRNA (5, 6). Othermodified nucleosides in rRNA not included in these categoriesare dihydrouridine in E.coli 23S rRNA (7