RESUMO
UGA remains an enigma as a signal in protein synthesis. Long recognized as a stop signal that is prone to failure when under competition from near cognate events, there was growing belief that there might be functional significance in the production of small amounts of extended proteins. This view has been reinforced with the discovery that UGA is found at some recoding sites where frameshifting occurs as a regulatory mechanism for controlling the gene expression of specific proteins, and it also serves as the code for selenocysteine (Sec), the 21st amino acid. Why does UGA among the stop signals play this role specifically, and how does it escape being used to stop protein synthesis efficiently at recoding sites involving Sec incorporation or shifts to a new translational frame? These issues concerning the UGA stop signals are discussed in this review.
Assuntos
Códon de Terminação/genética , Biossíntese de Proteínas , Animais , Bactérias/genética , Sequência de Bases , Evolução Molecular , Mudança da Fase de Leitura do Gene Ribossômico , Código Genético , Modelos Biológicos , Dados de Sequência Molecular , Inibidores da Ornitina Descarboxilase , Terminação Traducional da Cadeia Peptídica , Fatores de Terminação de Peptídeos/genética , Proteínas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Selenocisteína/genéticaRESUMO
AIM: To investigate a unique and critical step in retroviral gene expression not yet targeted for anti-viral therapy and to validate its potential as a site for anti-HIV intervention with a new group of therapeutic drugs. METHODS: A reporter system was designed using recombinant DNA methods to include sequence elements mediating translational frameshifting from HIV-1 and human antizyme RNAs. A mammalian in vitro protein synthesis system was used to assess the ratio of two separate reporter products in the presence of several drugs that are known to affect ribosomal function. RESULTS: The strategy aimed at modulating the ratio of viral proteins by disrupting frameshifting. Of the drugs tested, cycloheximide at 1 microM was the most promising candidate, resulting in a 35% reduction in frameshifting efficiency at the HIV site in the reporter system. At this concentration cycloheximide did not significantly affect frameshifting at the human antizyme site (the only known human protein to use translational frameshifting in its synthesis), nor inhibit translational efficiency of cellular proteins in general. CONCLUSIONS: A new group of drugs like cycloheximide that modify viral protein ratios have the potential to add significantly to the control of HIV. Viruses may be less likely to escape control from such a drug since it is targeted to cellular components required by the virus for frameshifting rather than the viral frameshift sequence itself. The reporter system used in this study is amenable for the first stage testing of a wide range of drugs.
