Progress in programming spatiotemporal patterns and machine-assembly in cell-free protein expression systems

•Realizing reaction-diffusion equations is necessary for cell-free pattern formation.•Turnover, communication, nonlinearity and feedback enable controlled dynamic.•Cell-free protein expression provides means to study assembly coupled to synthesis.•Important steps towards functional self-replicating machines have been established. Building biological systems outside the cell is an emerging interdisciplinary research field aimed to study design principles, and to emulate biological functions for technology. Reconstructing programmable cellular functions, from assembly of protein/nucleic-acid machines to spatially distributed systems, requires implementing minimal systems of molecular interactions encoded in genes, source-sink protein expression dynamics, and materials platforms for reaction-diffusion scenarios. Here, we first review how molecular turnover mechanisms, combined with nonlinear interactions and feedback in cell-free gene networks enable programmable dynamic expression patterns in various compartments. We then describe recent work on spatially distributed protein expression reactions. Finally, we discuss progress and challenges in the study of programmable protein/nucleic-acid complexes.