Human cytomegalovirus (HCMV) can infect many organs and different cells in vivo. HCMV UL/b’ genes are not found in the laboratory strain AD169, but in clinical strains Toledo and Merlin. Based on bio-informatics analyses, at least 19 open reading frames (ORF) are predicted in this region. However, whether these genes exist and how they are like in clinical strains is still unclear. To answer this question, the sequences of the genes in HCMV UL/b’ region of Clinical Strains were amplified using gene specific primers and were sequenced by direct sequencing the amplicons. The results showed that genes UL139, UL144, UL146, and UL139 are more variable in clinical strains. Based on phylogenetic analyses, above genes were categorized into different subgroups. The predicted gene UL151 was rarely found in clinical strains. Although some polymorphisms were found in genes UL139, UL144, UL146, and UL139, the other genes in UL/b’ region were relatively conserved in clinical strains. Generally speaking, the genes in UL/b’ region are more unstable compared to the genes in other region of HCMV. Their variability has potential molecular fundament to affect the infectivity of the virus.
