There is increasing understanding that endocytosis and signalling are linked to each other. Signalling receptors are particularly interesting as cargoes which are precisely regulated through the process of endocytosis. However it is still not clear that how the overlap between endocytosis and signalling occurs mechanistically. Rme-6, a Rab5 GEF, is a potential candidate that is involved in the endocytosis of transferrin and EGFR and also the signalling pathway of Ang1-Tie2. The objective of this thesis was to investigate the structure/function relationship of hRme-6 to understand how it integrates trafficking and signalling processes.