Nonenzymatic, template-directed ligation of oligoribonucleotides is highly regioselective for the formation of 3'-5' phosphodiester bonds.
We have found that nonenzymatic, template-directed ligation reactions of oligoribonucleotides display high selectivity for the formation of 3'-5' rather than 2'-5' phosphodiester bonds.  Formation of the 3'-5'-linked product is favored regardless of the metal ion catalyst or the leaving group, and for several different ligation junction sequences.  The degree of selectivity depends on the leaving group:  the ratio of 3'-5'- to 2'-5'-linked products was 10-15:1 when the 5'-phosphate was activated as the imidazolide, and 60-80:1 when the 5'-phosphate was activated by the formation of a 5'-triphosphate.  Comparison of oligonucleotide ligation reactions with previously characterized single nucleotide primer extension reactions suggests that the strong preference for 3'-5'-linkages in oligonucleotide ligation is primarily due to occurence of ligation within the context of an extended Watston-Crick duplex.  The ability of RNA to correctly self-assemble by template-directed ligation is an intrinsic consequence of its chemical structure and need not be imposed by an external catalyst (i.e., an enzyme polymerase); RNA therefore provides a reasonable structural basis for a self-replicating system in a prebiological world.
Rohatgi
R
R
Department of Molecular Biology, Massachusetts General Hospital, Boston 02114, USA.
Bartel
D P
DP
Szostak
J W
JW
D001483:Base Sequence; D019143:Evolution, Molecular; D006868:Hydrolysis; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000737:chemistry; D009841:Oligonucleotides / Q000737:chemistry*; D009843:Oligoribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D012313:RNA / Q000138:chemical synthesis* / Q000737:chemistry; D016337:RNA, Catalytic / Q000138:chemical synthesis* / Q000737:chemistry; D013329:Structure-Activity Relationship; D013698:Templates, Genetic; D013997:Time Factors
D007093:Imidazoles; D009711:Nucleotides; D009841:Oligonucleotides; D009843:Oligoribonucleotides; D016337:RNA, Catalytic; D012313:RNA