Analysis of Protein-Protein Interactions During Cytomegalovirus Infection

A key area in the study of infection by cytomegalovirus (CMV), or that of any other virus, is to gain an understanding of the manner in which viral proteins interact with those of the host cell. The most widely used method to identify interactions between viral and cellular proteins in the infected cell is that of co-immunoprecipitation; lysates from infected cells are treated with antibody which recognises, say, a viral protein of interest, and the resulting immune complexes are then screened for the presence of a cellular protein of interest: the presence of the second protein in the immune complexes is indicative of an interaction between the two proteins in vivo. However, such interaction need not necessarily be direct, as immunoprecipitation of a viral protein that could interact with a single component of a multiprotein complex might be expected to co-precipitate all the proteins in that complex. Therefore assays might be said to demonstrate protein-protein associations in the cell, rather than direct interactions. The resolving power of co-immunoprecipitations is also limited in other respects. First, the success of the assay relies heavily on the quality of the immunological reagents used; it is also possible that antibody binding will actually disrupt the interaction to be studied.