After definition of the human genome, it has become an important task to perform research on up till now undefined open reading frames.
The goal represents the clarification of the primary structure and function of the novel proteins. By comparative expression analysis of normal versus tumour tissue, we could observe over expression of C20orf116 in multiple tumour tissues. Encouraged by these findings we decided to clone and characterize the non-defined transcript and translation product. Multiple tissue Northern blot analysis showed expression of the 1.35 kb transcript coding for 314 amino acids in liver, placenta and heart with less quantity in kidney and lung as well as in various regions of the central nervous system. After production of the recombinant protein in E. coli and insect cells, polyclonal and monoclonal antibodies against the C20orf116 gene product were generated.
This enabled us to demonstrate the protein expression in liver, kidney, pancreas, thyroid and brain. Sequence alignment identified a PCI-domain at the C-terminus of the C20orf116 gene product. The PCI-domain is characterized as a strong protein-protein interaction domain and is contained in several subunits of three well known large multisubunit protein complexes: the proteasome, the COP9 signalosome (CSN) and the translation initiation factor (eIF3). Differential centrifugation revealed presence of the protein within the nucleus but mainly at the peroxisomes/mitochondria, high density microsomes, plasma membrane and at less quantity in cytoplasm.
The finding to influence promoter driven luciferase activity suggests potential involvement of this protein in translation or transcription processes. Direct DNA binding could be ruled out by initial protein-DNA interaction assays.
The results obtained in this study allow us to hypothesize that the C20orf116 gene product might represent an up till now unidentified member of the CSN signalosome or takes part in the eIF3 complex.