Accurate and precise control of gene expression is critical for cell survival in order to respond to cellular stress and environmental stimuli. Gene activity is tightly regulated at the level of transcription and translation but mRNA export which links the two processes also plays key role in gene regulation. During RNA export, several specific proteins are recruited to the transcribed RNA molecule where they form an RNA-protein complex, called messenger Ribonucleoprotein Particle (mRNP). In our laboratory we are studying the nuclear function of Moesin, the single cytoskeletal actin-binding ERM protein in Drosophila melanogaster. ERMs (Ezrin, Radixin and Moesin) compose a highly conserved group of proteins and carry out many crucial cytoplasmic functions including reorganization of the actin cytoskeleton, cell survival, membrane dynamics or cell migration. Previously we demonstrated that the Moesin protein is present also in the nucleus where it shows clear co-localization with mRNA export factors. In a functional assay we observed the accumulation of total mRNA in the nucleus upon RNAi against moesin in cultured cells and in vivo as well, demonstrating that the inhibition of Moesin’s function impairs mRNA export. As the detailed molecular mechanism underlying the nuclear activity of Moesin is still not known, we aim to identify the nuclear protein interaction partners of Moesin in order to get a deeper insight into the role and significance played by the actin-binding ERM proteins in nuclear mRNA export. Methods: Immunostaining of larval polytene giant chromosomes, Drosophila cell culture, mass spectrometry analysis, protein co-immunoprecipitation Results: In the mass spectrometry analysis Moesin pulled down almost the entire Mediator complex which is a multisubunit protein complex function in gene expression regulation and mRNA export as well. Moesin also showed colocalization with Mediator proteins on Drosophila larval giant chromosomes. Furthermore, among the candidate nuclear interaction partners we identified several mRNP members and proteins involved in mRNA processing and export, and these hits we could confirm by protein co-immunoprecipitation. Conclusions: Mass spectrometry analysis verified by protein co-immunoprecipitation suggests that Moesin’s function is related to the NXF2-mediated mRNA export pathway as a possible new binding partner of the Mediator complex. In vitro assays will further confirm these protein interactions.