Identification and expression of a murine cytomegalovirus early gene coding for an Fc receptor

Several herpesviruses, including cytomegalovirus, induce receptors
for the Fc domain of murine immunoglobulin G (IgG) molecules. Viral
genes coding for these receptors have been characterized only for
alphaherpesviruses. In this report, we describe a new approach that
led to the identification of an Fc receptor (FcR) of murine
cytomegalovirus (MCMV). The Fc fragment of IgG precipitated
glycoproteins (gp) of 86 to 88 and 105 kDa from MCMV-infected
cells. Deglycosylation by endoglycosidase F resulted in a protein
with a molecular mass of 64 kDa. Injection of complete MCMV DNA or
of DNA fragments, and the subsequent testing of cytoplasmic binding
of IgG by immunofluorescence microscopy, was used to search for the
coding region in the MCMV genome. The gene was located in the
HindIII J fragment, map units 0.838 to 0.846, where an open reading
frame of 1,707 nucleotides predicts a gp of 569 amino acids with a
calculated molecular mass of 65 kDa. The sequence of this gp is
related to those of the gE proteins of herpes simplex virus type 1
and varicella-zoster virus. The defined length of the mRNA, 1,838
nucleotides, was in agreement with that of a 1.9-kb RNA expressed
throughout the replication cycle, starting at the early stages of
infection. Expression of the gene fcr1 by recombinant vaccinia
virus resulted in the synthesis of gp86/88 and gp105, each with FcR
properties, and the correct identification of the gene encoding the
FcR was confirmed by the DNA injection method.