Alphavirus replicase and regulatory RNA elements in host interactions and viral vector engineering.

Alphavirus-derived vector systems have been used for heterologous gene expression for nearly four decades, providing foundational insights into RNA virus replication, host interactions, and genome engineering. The recent success of conventional mRNA vaccines has intensified interest in leveraging the alphavirus replicase and its associated conserved sequence elements (CSEs) to develop self-amplifying mRNA (sa-mRNA) platforms characterized by more sustained antigen expression and dose-sparing. In this minireview, we summarize key advances that define the coordinated functions of the nonstructural proteins and CSEs in viral RNA synthesis and host modulation. We then contextualize the developmental milestones of alphavirus replicons that underpin modern sa-mRNA technologies. We further discuss emerging strategies to engineer replicase functions and RNA architecture in different sa-mRNA applications, while outlining critical gaps in alphavirus biology that currently constrain rational sa-mRNA design. Renewed investigation of nonstructural proteins and CSEs will accelerate optimization of next-generation sa-mRNA platforms and reinvigorate fundamental studies of alphavirus replication, evolution, and host adaptation.