The complete DNA sequence of the Smith strain of murine cytomegaloviru
s (MCMV) was determined from virion DNA by using a whole-genome shotgu
n approach. The genome has an overall G+C content of 58.7%, consists o
f 230,278 bp, and is arranged as a single unique sequence with short (
31-bp) terminal direct repeats and several short internal repeats. Sig
nificant similarity to the genome of the sequenced human cytomegalovir
us (HCMV) strain AD169 is evident, particularly for 78 open reading fr
ames encoded by the central part of the genome. There is a very simila
r distribution of G+C content across the two genomes. Sequences toward
the ends of the MCMV genome encode tandem arrays of homologous glycop
roteins (gps) arranged as two gene families. The left end encodes 15 g
ps that represent one family, and the right end encodes a different fa
mily of 11 gps. A homolog (m144) of cellular major histocompatibility
complex (MHC) class I genes is located at the end of the genome opposi
te the HCMV MHC class I homolog (UL18). G protein-coupled receptor (GC
R) homologs (M33 and M78) occur in positions congruent with two (UL33
and UL78) of the four putative HCMV GCR homologs. Counterparts of all
of the known enzyme homologs in HCMV are present in the MCMV genome, i
ncluding the phosphotransferase gene (M97), whose product phosphorylat
es ganciclovir in HCMV-infected cells, and the assembly protein (M80).