title: The human cytomegalovirus UL76 gene regulates the level of expression of the UL77 gene.
abstract: BACKGROUND
  Human cytomegalovirus (HCMV) can be reactivated under immunosuppressive conditions causing several fatal pneumonitis, hepatitis, retinitis, and gastrointestinal diseases. HCMV also causes deafness and mental retardation in neonates when primary infection has occurred during pregnancy. In the genome of HCMV at least 194 known open reading frames (ORFs) have been predicted, and approximately one-quarter, or 41 ORFs, are required for viral replication in cell culture. In contrast, the majority of the predicted ORFs are nonessential for viral replication in cell culture. However, it is also possible that these ORFs are required for the efficient viral replication in the host. The UL77 gene of HCMV is essential for viral replication and has a role in viral DNA packaging. The function of the upstream UL76 gene in the HCMV-infected cells is not understood. UL76 and UL77 are cistons on the same viral mRNA and a conventional 5' mRNA for UL77 has not been detected. The vast majority of eukaryotic mRNAs are monocistronic, i.e., they encode only a single protein.
  
  
  RESULTS
  To determine whether the UL76 ORF affects UL77 gene expression, we mutated UL76 by ORF frame-shifts, stop codons or deletion of the viral gene. The effect on UL77 protein expression was determined by either transfection of expression plasmids or infection with recombinant viruses. Mutation of UL76 ORF significantly increased the level of UL77 protein expression. However, deletion of UL76 upstream of the UL77 ORF had only marginal effects on viral growth.
  
  
  CONCLUSIONS
  While UL76 is not essential for viral replication, the UL76 ORF is involved in regulation of the level of UL77 protein expression in a manner dependent on the translation re-initiation. UL76 may fine-tune the UL77 expression for the efficient viral replication in the HCMV- infected cells.
authors.affiliation: Division of Virology, Aichi Cancer Center Research Institute, Kanokoden, Nagoya, Japan. hisomura@aichi-cc.jp
authors.forename: Hiroki
authors.initials: H
authors.lastname: Isomura
authors.forename: Mark F
authors.initials: MF
authors.lastname: Stinski
authors.forename: Takayuki
authors.initials: T
authors.lastname: Murata
authors.forename: Sanae
authors.initials: S
authors.lastname: Nakayama
authors.forename: Shigeki
authors.initials: S
authors.lastname: Chiba
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Akatsuka
authors.forename: Teru
authors.initials: T
authors.lastname: Kanda
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tsurumi
mesh_terms: D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016296:Mutagenesis; D009154:Mutation; D016366:Open Reading Frames; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015534:Trans-Activators; C415646:UL76 protein, cytomegalovirus; D014764:Viral Proteins