RESUMO
The presence of antisense transcripts has been described in a wide variety of eucaryotic organisms, with a diversity of implied biological functions in development, control of cell cycles, hormonal responses, control of proliferation, structure, viral replication, and others. Reports have suggested that this type of control may operate at different levels of genic expression, whether in transcription, maturation, transport, stability, or translation of a given trascript. It is evident that the expression of antisense RNA has true importance in Eukaryotes, as already established in prokaryotic organisms. The objective of the present review is to present the advances in the mechanics of regulation, and roles already established for the expressions of antisense RNA in eukaryotic organisms.
La presencia de transcritos antisentidos ha sido descrita en una amplia variedad de organismos eucariontes, implicados en una diversidad de funciones biológicas como el desarrollo, el control del ciclo celular, respuesta hormonal, control de la proliferación, estructura, replicación viral, etc. Los informes indican que este control puede darse a diversos niveles de la expresión génica, ya sea en la transcripción, maduración, transporte, estabilidad y traducción de un determinado transcrito. Es evidente que la expresión del ARN antisentido tiene una real importancia en eucariontes, como ya ha sido establecido en organismos procariontes. Esta revisión tiene como objetivo mostrar los avances en los mecanismos de regulación y roles ya establecidos de la expresión de ARN antisentidos en organismos eucariontes.
Assuntos
Humanos , Fatores de Iniciação em Eucariotos/genética , Oligorribonucleotídeos Antissenso , RNARESUMO
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 translation 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.