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.

Retrotransposons play major roles in the expression of 'host' genes (218) and in addition some derivatives have acquired a protein coding function important for their host (neofunctionalized) together with immobility and nevertheless utilize frameshifting in their expression. Two major gene families are derived from Ty3/Gypsy long terminal repeat (LTR) retrotransposons, PEG10 (Human Paternal Expression Gene 10, also known as EDR, embryonal carcinoma differentiation regulated) being in one of the families and PNMA related genes in the other. PEG10 is not expressed from the maternally derived gene. Its expression was shown to utilize frameshifting (219) and subsequent work identified the correct pseudoknot frameshift stimulator (220) . The frameshifting occurs at a very high level, 60%, in the later stages of developing placenta and is likely important (221) . Knock-out mutants of PEG10 are lethal at an early embryonic stage and PEG10 products have numerous effects including inhibiting apoptosis and mediating cell proliferation (222, 223) . Expression in adult tissues has been more difficult to demonstrate but it may also be expressed in the adrenal glands of mammals (224) .