Human cytomegalovirus UL21.5 gene is expressed as an "early-late" gene in cultured human fibroblasts.
The human cytomegalovirus (CMV) UL21.5 gene encodes a secreted glycoprotein of unknown function. Both the UL21.5 protein and mRNA accumulate in abundance at late stages of infection making the RNA an attractive target for diagnosis of active CMV infection. The UL21.5 was originally described as a 'spliced late' gene (SLG) (Rawlinson and Barrell, J. Virol. 67, 5502 (1993)). However, we found that the the UL21.5 mRNA was detectable in CMV-infected patients before the onset of CMV DNA replication (Boriskin et al., J. Clin. Virol., in press). Here, we re-examined the UL21.5 mRNA kinetic class in CMV-infected human fibroblast culture using a RNAse protection assay and RT-PCR. The UL21.5 mRNA was detectable before the "true late" UL75 RNA, was resistant to a CMV DNA replication inhibitor but moderately sensitive to inhibitors of protein synthesis. In the presence of protein synthesis inhibitors the UL21.5 mRNA was detectable only by a nested reverse transcription - PCR (RT-PCR) with the bulk of it in unspliced form. This suggests that splicing factors for UL21.5 mRNA are encoded by the virus rather than by the cell. Our results indicate that UL21.5 should be defined as an "early-late" rather than a "late" (L) CMV gene.
Boriskin
Y S
YS
Department of Medical Microbiology, St. George's Hospital Medical School, London, UK. yboriski@sghms.ac.uk
Butcher
P D
PD
D000956:Antigens, Viral / Q000235:genetics; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000235:genetics*; D005347:Fibroblasts / Q000821:virology*; D005814:Genes, Viral; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics; D014158:Transcription, Genetic
D000956:Antigens, Viral; D017874:Immediate-Early Proteins; C044582:immediate-early proteins, cytomegalovirus