Protein synthesis in eukaryotes: The growing biological relevance of cap-independent translation initiation
MARCELO LÓPEZ-LASTRA1,2,*, ANDREA RIVAS1 and MARÍA INÉS BARRÍA1
1 Laboratorio de Virología Molecular, Centro de Investigaciones Médicas, Santiago, Chile.
2 Departamento de Pediatría Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Ribosome recruitment to eukaryotic mRNAs is generally thought to occur by a scanning mechanism, whereby the 40S ribosomal subunit binds in the vicinity of the 5'cap structure of the mRNA and scans until an AUG codon is encountered in an appropriate sequence context. Study of the picornaviruses allowed the characterization of an alternative mechanism of traslation initiation. Picornaviruses can initiate translation via an internal ribosome entry segment (IRES), an RNA structure that directly recruits the 40S ribosomal subunits in a cap and 5' end independent fashion. Since its discovery, the notion of IRESs has extended to a number of different virus families and cellular RNAs. This review summarizes features of both cap-dependent and IRES-dependent mechanisms of translation initiation and discusses the role of cis-acting elements, which include the 5'cap, the 5'-untranslated region (UTR) and the poly(A) tail as well as the possible roles of IRESs as part of a cellular stress response mechanism and in the virus replication cycle.
Key terms: protein synthesis, translation initiation, internal ribosome entry segment
Source: Biol Res. 2005;38(2-3):121-46.