Characterization of the murine cytomegalovirus genes encoding the major DNA binding protein and the ICP18.5 homolog

In several herpesviruses the genes for the major DNA binding
protein (MDBP), a putative assembly protein, the glycoprotein B
(gB), and the viral DNA polymerase (pol) coliocate. In murine
cytomegalovirus (MCMV), two members of this gene block, pol
(Elliott, Clark, Jaquish, and Spector, 1991, Virology 185, 169-186)
and gB (Rapp, Messerle, BOhler, Tannheimer, Keil, and Koszinowski,
1992, J. Virol., 66,4399-4406) have been characterized. Here the
two other MCMV genes are characterized, the gene encoding the MDBP
and the ICP18.5 homolog encoding a putative assembly protein. Like
in human cytomegalovirus (HCMV) the genes order is pol, gB,
ICP18.5, and MDBP. The 4.2-kb MDBP mRNA is expressed first in the
early phase, whereas the 3.0-kb ICP18.5 mRNA is a late transcript.
The open reading frame of the MDBP gene has the capacity of
encoding a protein of 1191 amino acids with a predicted molecular
mass of 131.7 kDa. The MCMV ICP18.5 ORF is translated into a
polypeptide of 798 amino acids with a calculated molecular mass of
89.1 kDa. Comparison of the amino acid sequences of the predicted
proteins of MCMV with the respective proteins of HCMV, Epstein-Barr
virus (EBV), and herpes simplex virus type-1 (HSV-1) reveals a
striking homology ranging from 72% (HCMV), 50% (EBV), to 45%
(HSV-1) for the MDBP sequence and from 74% (HCMV), 51 % (EBV), to
49% (HSV-1) for the ICP18.5 sequence. These results establish the
elose relationship of the two cytomegaloviruses, and underline the
usefulness of the murine model for studies on the biology of the
CMV infection.