The present disclosure generally relates to viral-based expression systems suitable for the production of molecule of interests in recombinant host cells. The disclosure particularly relates to nucleic acid constructs, such as expression vectors, containing a modified arterivirus genome or replicon RNA in which at least some of its original viral sequence has been deleted. Also included in the disclosure are viral-based expression vectors including one or more expression cassettes encoding heterologous polypeptides. In some embodiments, the expression cassettes are configured and positioned at defined locations on the viral genome so as to enable expression of the heterologous polypeptides in a tunable manner.