Ribosomal frameshifting and transcriptional slippage: From genetic steganography and cryptography to adventitious use

Atkins, John F.; Loughran, Gary; Bhatt, Pramod R.; Firth, Andrew E.; Baranov, Pavel V.

To minimize the need for a proto ribosome to stabilize triplet codon: anticodon interactions, Crick and colleagues developed a proto tRNA anticodon alternating stacking scheme that allowed for quintuplet pairing but only triplet decoding thus avoiding destruction of previously coded information on transition to triplet only pairing (726) . Despite the elegance of this scheme, several of the different models for the origin of decoding are relevant for those with the mindset of a less sacrosanct view of framing and an appreciation that Crick's frozen accident thesis (727) has considerably melted (728) . These models involve stereochemical interactions between amino acids and RNA, proto mR-NAs evolving as linkers between peptidated RNAs and tR-NAs derived from replicators involving parallel duplication (729) (730) (731) . Further to the framing latitude considered in the last paragraph due to dissociation and re-pairing, there has been consideration of greater than triplet codon: anticodon interactions by proto tRNAs (722, 723) , and perhaps even of tRNA mimics (486) . While at least the great majority of frameshifting with WT translational components considered above involves at least one tRNA anticodon dissociating and re-pairing in a new frame, that of Ty3 has been proposed not to do so (214) and there is considerable doubt about a case of non-cognate frameshifting (452, 453) . Similarily among the frameshift mutant suppressors that have altered tRNAs, though some involve anticodon racheting, in at least the great majority the evidence points to no more than 3 anticodon loop nts being paired to mRNA at one time (440, 732) .