Biology Reference
In-Depth Information
Fig. 2
CMV chemokine and chemokine receptor homolog gene loci. The central line represents
the HCMV Merlin strain genome (235,645 kb) derived from GenBank accession NC_006273.
The
black boxes
on this line represent repetitive regions. The chemokine homolog gene loci are
enlarged above the genomic line, the chemokine receptor homolog gene loci below the genomic
line. The
arrowheads
indicate the sizes and directions of the coding content of the genes. The
UL128 exon sizes and positions are analogous to those of the HCMV AD169 strain, as indicated
in NC_006273.
UL
unique long,
US
unique short
genes. Similar to the UL33- and UL78-like genes, the UL128-like chemokine genes
are likely to have been acquired by betaherpesviruses at least 110 My ago. The
conservation of this gene family suggests an essential role for these genes in the
survival of betaherpesviruses in vivo. This notion is supported by the observation
that the UL128 sequences from different clinical HCMV isolates are highly
conserved (Baldanti et al. 2006). Paradoxically, the UL128 gene appears to be
functional in laboratory strain HCMV AD169, whereas in the clinical, low-passage
HCMV strains Toledo and Merlin, as well as in the chimpanzee CMV (CCMV)
laboratory strain, the UL128-like genes are disrupted by inversions or frame shift
mutations (Table 1). A UL128 counterpart was also identified on the HHV-6
genome, designated U83A. This gene was found to encode a potent CC chemokine
(Derwin et al. 2006). Interestingly, the UL130 genes of the primate CMVs also
contain chemokine-like sequences, including a CXC domain (Glass et al. 2003).
However, the UL130-derived amino acid sequences lack other cysteine residues
that are essential for classical chemokine folding (Glass et al. 2003). The MCMV
and RCMV genome sequences available to date do not contain UL130-like CXC
chemokine sequences. Nevertheless, within the genome of the Maastricht strain of
RCMV, a second CC chemokine-like gene, r131, was identified adjacent to r129.
These two genes may have originated from duplication of a common ancestor gene
(Kaptein et al. 2004; Voigt et al. 2005). In contrast to the UL128-like genes, UL146
and UL147 appear to be restricted to the primate CMVs. Both the HCMV and
CCMV UL146 genes encode a CXC vCK (Table 1). Rhesus macaque CMV
(RhCMV) does not possess a UL146 homolog (Table 1). Both the HCMV and
CCMV genomes contain a UL147 gene, whereas a UL147-like gene is present in
