A MOUSE CYTOMEGALOVIRUS GLYCOPROTEIN, GP34, FORMS A COMPLEX WITH FOLDED CLASS-I MHC MOLECULES IN THE ER WHICH IS NOT RETAINED BUT IS TRANSPORTED TO THE CELL-SURFACE

Murine cytomegalovirus (MCMV) interferes with antigen presentation by means of retaining major histocompatibility complex (MHC) class I mole cules in the endoplasmic reticulum (ER). Here we identify and characte rize an MCMV-encoded glycoprotein, gp34, which tightly associates with properly conformed MHC class I molecules in the ER. Gp34 is synthesiz ed in large quantities during MCMV infection and it leaves the ER only in association with MHC class I complexes. Many but not all class I m olecules are retained in the ER during the early phase of MCMV infecti on, and we observe an inverse correlation between amounts of gp34 synt hesized during the course of infection and class I retention. An MCMV deletion mutant lacking several genes, including the gene encoding gp3 4, shows increased class I retention. Thus, MCMV gp34 may counteract c lass I retention, perhaps to decrease susceptibility of infected cells to recognition by natural killer cells.