Abstract
We describe the nonenzymatic ligation of RNA oligomers in water. Dimers and tetramers are formed in a time-, pH-, and temperature-dependent reaction. Ligation efficiency depends on oligonucleotide length and sequence and is strongly enhanced by adenine-based nucleotide cofactors. Ligation of short RNA fragments could have liberated the prebiotic polymerization systems from the thermodynamically demanding task of reaching a (pre)genetically meaningful size by stepwise addition of one precursor monomer at the time.