#$%^&*AU2014101350A420141211.pdf#####- 16ABSTRACT The invention provides, inter alia, isolated nucleic acid molecules encoding a positive strand self-replicating RNA and further comprising at least two heterologous small moleculeresponsive aptamers. In related aspects, the invention also provides methods of controllably regulating gene expression (e.g., of an immunogen) by modulating the levels of the small molecule to which the small molecule-responsive aptamer binds.