Chemical synthesis of oligonucleotides

All oligonucleotides were synthesized on an automated RNA/DNA synthesizer using standard phosphoramidite chemistry [19]. The deprotection and purification of unmodified oligoribonucleotides or TBA variants containing UNA-iG and RNA-iG were performed according to general procedures. Deprotection of TBA variants modified simultaneously with RNA-s4U and RNA-iG or UNA-s4U and UNA-iG was performed by the treatment with methanol/aqueous ammonia solution (1:1 v/v) at room temperature for 48 h. The purification was accomplished according to previously published procedures [20]. The composition of all oligonucleotides was confirmed by MALDI-TOF mass spectrometry.