RNA replicon for versatile and efficient gene expression

The present invention embraces an RNA replicon (self-amplifying RNA vector (saRNA)) that can be replicated by a replicase of a self-replicating virus, e.g., a replicase of alphavirus origin. According to the invention, translation of the replicase open reading frame is uncoupled from a 5'-terminal cap by placing translation of the replicase open reading frame under the translational control of an internal ribosome entry site (IRES). Thereby the initiation of translation depends on the molecular properties of the respective IRES, which compared to cap-dependent translation may require less or no cellular initiation factors to direct the ribosome to the translational start site. According to the invention, IRES-controlled replicase translation may allow the use of uncapped synthetic saRNA. Furthermore, the use of an IRES provides for the option to insert additional transgenes upstream to the IRES.