Characterization of an Antisense Transcript Spanning the UL81-82 Locus of Human Cytomegalovirus

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Abstract
In this study we present the characterization of a novel transcript, UL81-82ast, UL81-82 antisense transcript, and its protein product. The transcript was initially found in a cDNA library of monocytes from a seropositive donor. mRNA was obtained from monocytes isolated from a healthy donor with a high antibody titer against human cytomegalovirus (HCMV). The mRNAs were cloned into a lambda phage-derived vector to create the cDNA library. Using PCR, UL81-82ast was amplified from the library. The library was tested for the presence of numerous HCMV genes. Neither structural genes nor immediate-early genes were found. UL81-82ast was detected in five bone marrow samples from healthy antibody-positive donors. This same transcript was also found in in vitro-infected human fibroblasts early after infection but disappears at the same time that UL82 transcription begins. Not only was the transcript amplified using reverse transcription-PCR and sequenced but its protein product (UL82as protein) was detected by both Western blot and immunofluorescence. Phylogenetic studies using UL82as protein were conducted, showing a high degree of conservation in clinical isolates, laboratory strains of HCMV, and even in chimpanzee CMV. The transcript could be involved in the posttranscriptional regulation of the UL82 gene, affecting its mRNA stability or translation. Since the UL82 product, pp71, functions as an immediate-early transactivator, its posttranscriptional control could have some effect over latency reactivation and lytic replication.