Shunting is a translation strategy used by plant pararetroviruses (Caulimoviridae)

In eukaryotes standard initiation of translation involved 40S ribosome scan ning to bridge the distance from the cap to the initiation codon. Recently deviations from that rule had been described, including "internal initiatio n", "poly-A dependent translation", and "ribosome shunting". In ribosome sh unting, ribosomes start scanning at the cap but large portions of the leade r are skipped. Thereby the secondary structure of the shunted region is pre served. Scanning in plant caulimoviruses involve a small open reading frame properly spaced in front of a strong stem structure, and, in order to func tion, the small open reading frome has to be translated and the peptide rel eased. This arrangement can be mimicked by artificial small open reading fr ames and stem structures. Shunting with viral and synthetic leaders occurs not only in plant-, but also in mammalian and yeast systems. Thus it respon ds to an intrinsic property of the eukaryotic translational machinery and p robably acts in many cases where coding regions are preceded by complex lea ders. (C) 2000 Elsevier Science Ltd. All rights reserved.