The non-canonical nucleotides and prebiotic evolution

The mystery of the origin of life has been puzzling mankind for several millenia. Starting from the second half of the 20^th century, when the crucial role of nucleic acids in biological heredity became apparent, the emphasis in the field has shifted to the explanation of the origin of nucleic acids and the mechanisms of copying of macromolecules. In the 1960s, the hypothesis of the RNA World was proposed, according to which the first stages of the origin of life on Earth were associated with the appearance of self-replicating complexes based on RNA, that were akin to RNA-enzymes that catalyze critical for life chemical reactions. Currently, it has been shown that different forms of RNA include not only canonical (adenine, uracil, guanine, cytosine), but also about 170 non-canonical nucleotides. In this review, we discuss potential roles of these non-canonical nucleotides in the processes of molecular prebiotic evolution, such as the emergence of canonical RNA nucleotides and catalytic RNAs, as well as the origin of template synthesis of RNA and proteins.