In the post-genomic area new approaches have been developed to study and characterize protein functions in cells and organisms. One such strategy is the yeast two-hybrid system that can be used to generate complete protein interactions maps. Infectious pancreatic necrosis is one o the most threatening diseases in Norwegian aquaculture, and the disease has a worldwide distribution. The causative agent of this disease is infectious pancreatic necrosis virus (IPNV), a prototype virus of the Birnaviridae f amliy. The virus has a double-straned RNA genome divides into two segments and encodes 5 proteins (VP1 to 5). Certainly one of the most important and challenging problems in IPNV biology is defeining a host environment and the specific factors, both in host and virus, required for infectious virus production and persistaence. The aim of this project is to use the yeast-two hybrid system combined with pull-down experiments to examine potential interactions betweeen all IPNV proteins and in addition interactions between VP3 and viral RNA. Furthermore the yeast two-hybrid screening will be extended to map interactions between IPNV proteins and hos cell defence proteins using a whole library approach. Crystallization of VP2 and VP3 wi ll be attempted for the purpose of resolving their structures by X-ray crystallography.