Human cytomegalovirus (HCMV), a ubiquitous human pathogen, is the leading cause of birth defects in newborns. A region (referred to as UL/b′) present in the Toledo strain of HCMV and low-passage clinical isolates) contains 22 additional genes, which are absent in the highly passaged laboratory strain AD169. One of these genes, UL145 open reading frame (ORF), is located between the highly variable genes UL144 and UL146. To assess the structure of the UL145 gene, the UL145 ORF was amplified by PCR and sequenced from 16 low-passage clinical isolates and 15 non-passage strains from suspected congenitally infected infants. Nine UL145 sequences previously published in the GenBank were used for sequence comparison. The identities of the gene and the similarities of its putative protein among all strains were 95.9–100% and 96.6–100%, respectively. The post-translational modification motifs of the UL145 putative protein in clinical strains were conserved, comprising the protein kinase C phosphorylation motif (PKC) and casein kinase II phosphorylation site (CK-II). We conclude that the structure of the UL145 gene and its putative protein are relatively conserved among clinical strains, irrespective of whether the strains come from patients with different manifestations, from different areas of the world, or were passaged or not in human embryonic lung fibroblast (HELF) cells.

Human cytomegalovirus (HCMV) mRNA was obtained from human embryonic lung fibroblast cells infected by HCMV clinical strains from urine samples of infants at different kinetic periods. The cDNA of UL131A-128 mRNAs was amplified using reverse transcription-polymerase chain reaction (RT-PCR) and analysed by sequencing. Mean while, clones containing UL131A-128 transcripts in an HCMV cDNA library of a clinical strain were selected and sequenced. It was demonstrated that UL131A-128 mRNA was expressed with immediately early, early and late kinetics. Sequences obtained by RT-PCR showed that the UL131A gene consisted of two exons and the coding region of the UL130 gene was not interrupted by any intron in the region as reported earlier. However, the transcript of the UL128 gene showed two patterns: one pattern consisted of three exons as reported earlier; the other contained the three exons and also the first intron. Moreover, the above characteristics of UL131A-128 spliced transcripts were confirmed by the sequences of clones selected from the HCMV cDNA library. Our results demonstrated that the UL131A, UL130 and UL128 genes were transcribed with the 3′-coterminal, although the initiation points of their mRNA may be different. The variation in the transcripts found in our study indicated the complex nature of transcription of UL131A-128 genes in clinical strains of HCMV.

MicroRNAs (miRNAs) are small RNAs, 19–23 nucleotides in length, which regulate a variety of cellular processes. Human cytomegalovirus (HCMV) encodes only one intronic miRNA: human cytomegalovirus microRNA UL36 (hcmv-miR-UL36). In this study, we found that over-expression of hcmv-miR-UL36 resulted in a more than threefold increase in HCMV DNA synthesis at 24 h post infection. Fifteen putative targets of hcmv-miR-UL36 were identified using hybrid PCR, one being the HCMV UL138 gene that has previously been identified as a novel latency-associated determinant of HCMV infection. Down-regulation of UL138 expression by hcmv-miR-UL36 was validated using luciferase reporter assays and Western blot analysis in HEK293 cells. In the presence of hcmv-miR-UL36, we observed a 74.6% decrease in luciferase activity and a 46.2% decrease in HCMV UL138 protein expression. Our results indicate that hcmv-miR-UL36 may be a viral miRNA contributing to HCMV replication.