Morphology and Distribution of gp52 on Extracellular Human Cytomegalovirus (HCMV) Supports Biochemical Evidence that It Represents the HCMV Glycoprotein B

1 Department of Medical Microbiology, University of Cape Town Medical School, Observatory, Cape Town, South Africa 7925 and 2 Division of Pathology, Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire SP4 0JG, U.K. Glycoprotein gp52 exists within the mature human cytomegalovirus (HCMV) envelope in heterodimeric, disulphide-linked complexes with glycoproteins gp95 and gp130. Biochemical studies involving immunoprecipitations and Western blots have demonstrated that gp52 is the glycoprotein B (gB) homologue of HCMV but that gp95 and gp130 are probably separate gene products. The distribution of this putative gB on extracellular HCMV particles was revealed by high resolution electron microscopy of preparations labelled with a monoclonal antibody, F5, directly coupled to colloidal gold. F5-gold probes, specific for HCMV gp52, bind to the distal end of 12 nm long, slender spikes projecting from virion and dense body envelopes. Labelled spikes were most often present in closely packed, homogeneous clusters and were frequently present on envelope protrusions. The degree of labelling on individual HCMV particles was highly variable. Both the morphology and distribution of HCMV gp52 show strong similarity with that previously reported for the gB of herpes simplex virus. Other morphologically distinct spikes occur in the HCMV envelope but these were not recognized by F5—gold probes. Keywords: cytomegalovirus, glycoprotein B, immunogold label Received 4 October 1988; accepted 13 February 1989.