[RNA-ligase of bacteriophage T4. IV. Synthesis of pentadecaribonucleotide ApUpG(pU)6(pA)5pAp].

Oligoribonucleotide ApUpG(pU)6(pA)5pAp (I) has been prepared by means of RNA ligase. ApUpG, synthesised by the phosphotriester approach, was elongated in the 3'-direction by adding (pU)6 and then (pA)6, which was 3'-blocked with the phosphate or with the periodate-oxidized AMP residue, the latter giving considerably lower level of by-products. Condensation of ApUpG(pU)6 with blocked (pA)6 was carried out under conditions optimal for poor acceptors (20 degrees C, 48 h, pH 8,7) to afford (I) with the yield of 20% (105 OE260); ApUpG(pU)6(pA)10pAp was identified as a byproduct.