Chemical Synthesis of 4-Thiouridine-Containing Substrate Analogues of tRNA:Pseudouridine-55 Synthase: Photocross-Linking Studies

Abstract

For site specific incorporation of 4-thiouridine into oligoribonucleotides a new phosphoramidite is proposed. It makes use of the S-pivaloyloxymethyl group for the protection of the thiol function. This group is easily introduced and removed without modification of the standard protocol for solid phase synthesis of RNA. Three 4-thiouridine-containing oligoribonucleotides (21-mers), corresponding to tRNA minisubstrates of yeast tRNA:pseudouridine-55 synthase (Pus4) were prepared. These 4-thiouridine containing substrates were characterized and used as photoaffinity probe of the enzyme:substrate complex. Irradiation resulted in the specific photocross-linking of these oligoribonucleotides with purified recombinant tRNA:pseudouridine-55 synthase.