CHARACTERIZATION OF A NOVEL 3RD MEMBER OF THE HUMAN CYTOMEGALOVIRUS GLYCOPROTEIN-H GLYCOPROTEIN-L COMPLEX

A prerequisite for understanding the molecular function of the human c ytomegalovirus (HCMV) gH (UL75)-gL (UL115) complex is a detailed knowl edge of the structure of this complex in its functional form, as it is present in mature virions, The gH protein is known to be a component of a 240-kDa envelope complex designated as gCIII (D. R. Gretch, B. Ka ri, L. Rasmussen, R. C. Gehrz, and M. F. Stinski, J. Virol. 62:875-881 , 1988), However, the exact composition of the gCIII complex remains u nknown. In this report, we attempted reconstitution of the gCIII compl ex by coexpression of gH and gL in the baculovirus expression system, Formation of recombinant gH-gL complexes of approximately 115 kDa was demonstrated; however, no higher-molecular-mass (similar to 240-kDa) r ecombinant gH-gL complexes were detected, suggesting that the presence of gH and gL alone is not sufficient for reconstitution of the gCIII complex, To identify other mammalian and/or HCMV factors which may be necessary for gCIII formation, immunoprecipitates of gH and gL from HC MV-infected fibroblasts and purified HCMV virions were examined. This analysis did reveal a number of coprecipitating proteins which associa te either transiently or integrally with gH and gL. One coprecipitatin g protein of 145 kDa was shown to be an integral component of gCIII, a long with gH and gL, Characterization of the 145-kDa protein demonstra tes that it is structurally and antigenically unrelated to gH and gL a nd that it appears to be virally encoded, Together, these data indicat e that the 145-kDa protein is a third novel component of the mature HC MV gH-gL complex.