A positive-selection function for microRNA: an adaptor hypothesis revisited

A hypothesis for coding different combinations of mRNA segments by a novel postulated function of microRNAs (miRNA) is presented. In this hypothesis, miRNA act as both coding adaptors and ligating enzymes. This hypothesis postulates an enzyme–substrate intermediate comprising a RNA triplex structure consisting of a miRNA adaptor and two mRNA configured as two turns of an A-form RNA helix. Postulating the existence of differentially expressed sets of adaptors (codes) may explain biological functions such as imprinting, differentiation, immunological escape and immunological tolerance, inter alia.