Non-Watson-Crick RNA synthesis suited to origin functions

Abstract

A templated RNA synthesis is characterized in which G5’pp5’G accelerates synthesis of A5’pp5’A from pA and chemically activated ImpA precursors. Similar acceleration is not observable in the presence of UppU, CppC, AppG, AppA or pG alone. Thus, it seems likely that AppA is templated by GppG via a form or forms of G:A base-pairing. AppA also appears, more slowly, via a previously known untemplated 2nd order chemical route. Such AppA synthesis requires only ordinary near-neutral solutions containing monovalent and divalent salts, and rates are only slightly sensitive to variation in pH. Templated synthesis rates are 1st order in pA, ImpA and template GppG; thus 3rd order overall. Therefore this reaction resembles cross-templating of AppA on poly (U), but is notably slower and less sensitive to temperature. Viewing AppA as a coenzyme analogue, GppG templating provides a simpler molecular route, termed para-templating, to encoded chemical functions. Para-templating can also arise from a single, localized nucleobase geosynthetic event which yields purines. It also requires a single backbone-forming chemistry. Thus it may have appeared earlier and served as evolutionary precursor for more complex forms of encoded genetic expression.