Human Cytomegalovirus ICP22, the Product of the HWLF1 Reading Frame, Is an Early Nuclear Protein that Is Released from Cells

Abstract

Summary We employed a murine monoclonal antibody (CH41) and a λgt11 library of human cytomegalovirus (CMV) DNA fragments to map the gene for a viral protein, denoted infected cell protein (ICP) 22, to the HWLF1 open reading frame in the S component of the CMV genome (0.92 to 0.93 map units). By using antibody CH41 in immunofluorescence, immunoprecipitation and immunoblotting analyses, ICP22 was readily detected as a β (delayed early) gene product during viral growth. The cellular localization of this protein was found to be nuclear by immunofluorescence analysis; however, it partitioned with the cytoplasm when cells were fractionated with non-ionic detergents. Analysis of cell-free medium showed that a proportion of ICP22 was released from cells as a soluble protein at both early (24 h) and late (72 to 120 h) times in infection. The function of this protein which has such diverse characteristics remains unknown.