| Human cytomegalovirus (HCMV) is a medically significant pathogen responsible for causing incapacitating and life-threatening diseases in immunocompromised and immunosuppressed individuals. HCMV gene expression is temporally regulated and the immediate-early genes, the first genes to be transcribed, are essential for viral growth, are anti-apoptotic and involved in viral DNA replication. In spite of being regulated by the same promoter, immediate-early UL37 mRNAs are differentially expressed during permissive HCMV infection.;The HCMV UL37x1 unspliced mRNA, whose production requires use of an internal polyadenylation site located within intron 1, is abundantly expressed throughout infection and encodes an essential protein, pUL37x1. In contrast, UL37 alternatively spliced mRNAs, are of lower abundance and differentially produced during immediate-early, early, or late times of infection. Furthermore, the ratio of UL37x1 unspliced mRNAs increases over alternatively spliced UL37 mRNAs as infection progresses. This temporal and differential regulation of alternatively processed UL37 mRNAs suggests a finely tuned modulation of UL37 pre-mRNA post-transcriptional processing during infection.;Post-transcriptional processing is dynamic and requires activation and recruitment of processing machineries to sites of transcription. This process is highly regulated and requires the interaction, relocalization and activation of numerous cellular proteins. Previous studies conducted by this laboratory confirmed that HCMV infection increases the abundance of critical cellular post-transcriptional processing factors and induces key alterations in several cellular regulators of these factors. Moreover, several of these HCMV-induced factors were found to have regulatory control over production of UL37 alternatively processed mRNAs. The goal of this study was to understand the mechanisms through which HCMV manipulates host cell pre-mRNA processing machineries to favor production of UL37x1 unspliced transcripts.;To that end, we examined the localization of essential splicing and polyadenylation factors over the course of the HCMV lytic replication cycle. We found that HCMV infection induces temporal and spatial relocalization of essential pre-mRNA processing factors and regulators of post-transcriptional processing factors to predictably favor production of HCMV transcripts. Unexpectedly, we observed that during late times of infection, an essential polyadenylation factor, CstF-64, localizes to HCMV viral replication compartments. This discovery lead us to identify the process through which mature HCMV viral replication compartments are formed. |
