MicroRNAs are a recently discovered class of small non-coding RNAs that act as post-transcriptional regulators of gene expression by silencing target mRNAs. They have wide ranging roles in many cellular processes including cellular proliferation, stress response, apoptosis, development and differentiation. Altered expression of microRNA has been implicated in tumorigenesis, and microRNAs are recognised as modulating factors in numerous cancers including gastric cancer, lung cancer and lymphocytic leukaemia. Specifically, microRNA functions within the cytoplasm in concert with the human-induced silencing complex by binding the 3’ untranslated region of the target mRNA. This binding to target mRNA effectively inhibits expression of the protein, and thus mediates the gene silencing effect of microRNA. This project aims to elucidate the structure and biophysical basis of the nuclear export complex formed by pre-microRNA (precursor of microRNA), RanGTP and exportin-5. These goals will be achieved using a combination of structural, biochemical and biophysical approaches. X-ray crystallography and nuclear magnetic resonance will be utilised to study the structure of the export complex of microRNA. In parallel with the determination of the complex structure, the key residues involved in complex formation will be identified by mutagenesis, cross-linking and further NMR approaches. Furthermore, a range of biophysical techniques will be employed to study the thermodynamic and kinetic basis for the formation of the microRNA export complex. The information provided by this study will be of the highest international standard and will open novel avenues to therapeutic design as well as represent a significant advance in our understanding of cellular biology. Importantly, it will provide a platform for knowledge sharing and collaboration between a European based organization and a top-class non European researcher.