This protocol describes the transfection of mammalian cells with in vitro transcribed, unmodified, non-charged tRNAs. We have used this method successfully to raise intrinsic tRNA concentrations in HeLa1 and N2a cells2. Furthermore, tRNAs synthesised as described in this protocol have been shown to be translation competent1.References1. Kirchner et al. Alteration of Protein Function by a Silent Polymorphism Linked to tRNA Abundance. PLoS Biology. 2017, in press.2. Girstmair et al. Depletion of Cognate Charged Transfer RNA Causes Translational Frameshifting within the Expanded CAG Stretch in Huntingtin. Cell Reports. 2013, 3(1):148-59. DOI: http://dx.doi.org/10.1016/j.celrep.2012.12.019