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.

Bacterial release factor 2 (RF2) mediates termination at UGA and UAA, with its termination at UGA being unique since bacterial release factor 1 mediates termination at UAG and UAA. Before their genes were sequenced the possibility was entertained that the coding sequence for RF2 might have an in-frame UGA stop codon early in the coding sequence with deficiency of RF2 leading to extra slow decoding of UGA that facilitated stop codon readthrough by near-cognate tRNA resulting in synthesis of full-length RF2. However, none of the RF2 genes from the large number of sequenced bacterial genes have such an early in-frame UGA codon (348) with ORF2 continuing in the same frame and the counterpart with UAG and release factor 1 genes is also unknown. [A giant virus of amoeba does have a release factor gene whose expression involves stop codon readthrough and separately ribosomal frameshifting (349) .]