DNA has been recently used to construct a variety of nanoscale machines and switches, among them devices which can translocate, compute, or bind and release molecules. For future applications it is interesting to investigate whether these "artificial" functions can also be implemented in vivo. As one step towards in vivo applications, we currently utilize RNA molecules for construction or control of molecular devices. RNA molecules can be transcribed from "artificial genes" and either fold into functional nanoassemblies themselves or drive other nucleic acid-based devices as a "fuel". Furthermore, coupling of nanomachines to RNA transcription enables control of their behavior using gene regulatory motifs.