Self-association and mapping of the interaction domain of hepatitis E virus ORF3 protein

Hepatitis E virus (HEV) is a major human pathogen in the developing world. In the absence of an in vitro culture system, very little information on th e basic biology of the virus exists. A small protein (similar to 13.5 kDa) of unknown function, pORF3, is encoded by the third open reading frame of H EV, The N-terminal region of pORF3 is associated with the cytoskeleton usin g one of its hydrophobic domains. The C-terminal half of pORF3 is rich in p roline residues and contains a putative src homology 3 (SH3) binding domain and a mitogen-activated protein kinase phosphorylation site. In this study , we demonstrate that pORF3 can homodimerize in vivo, using the yeast two-h ybrid system. We have isolated a 43-amino-acid interaction domain of pORF3 which is capable of self-association in vivo and in vitro. The overlap of t he dimerization domain with the SH3 binding and phosphorylation domains sug gests that pORF3 may have a dimerization-dependent regulatory role to play in the signal transduction pathway.