Patterns of Transcription of Human Cytomegalovirus in Permissively Infected Cells

Abstract

The rate of accumulation of cytomegalovirus transcripts in permissively infected human embryonic lung (HEL) cells was analyzed at various times after infection by hybridization of infected cell RNA to undigested or restriction endonuclease-digested cytomegalovirus DNA fixed to nitrocellulose filters. Differences in patterns of transcript accumulation were determined by measuring the abundance levels of RNA which hybridized to different HindIII-, XbaI-, or EcoRI-generated fragments of cytomegalovirus DNA. The results showed that a small but significant amount of cytomegalovirus RNA was detectable within the first 3 h after infection and that the rate of accumulation of these transcripts was static during the first 24 h, but increased thereafter. In general, the viral transcripts accumulating in infected cells could be divided into three classes. Immediate-early RNA (synthesized in the absence of protein synthesis in infected cells) hybridizes predominantly to a very restricted part of the genome and can be identified during the first 2 to 4 h postinfection. Early RNA (synthesized up to about 24 h after infection) originates from most regions of the genome but is characterized by the presence of transcripts which hybridize in great abundance to certain fragments. Late RNA (synthesized after 24 h, i.e., after the onset of viral DNA synthesis) hybridizes in approximately equal abundance to most regions of the viral genome. These results showed that a block in the transition from immediate-early to early RNA did not account for the extended period of time that elapses between the time of infection and the initiation of viral DNA synthesis. Interestingly, despite rapid adsorption and penetration and a static level of accumulation of transcripts in the cultures during the first 24 h, the number of cells that synthesized detectable amounts of viral antigens increased steadily during this time.

The human cytomegalovirus UL98 gene transcription unit overlaps with the pp28 true late gene (UL99) and encodes a 58-kilodalton early protein

“…As in other herpesviruses, replication proceeds in a coordinated way, with characteristic classes of viral genes being expressed in a cascade-like manner. Three phases of virus gene expression occur, and they have been described as immediate early (IE), early, and late (5,22,40). From a broad perspective, IE genes are thought to be responsible for regulating the course of virus replication (reviewed in reference 32), early genes are responsible for DNA replication (reviewed in references 29 and 32), and late proteins are the structural compo-nents of the virus (reviewed in reference 8).…”

Inhibition of p53 transcriptional activity by human cytomegalovirus UL44

“…During productive infection, HCMV gene expression occurs in three temporarily regulated phases, termed the immediate early, early, and late phases (20)(21)(22)(23). p53 starts to be accumulated in normal host cells immediately after HCMV infection and increases thereafter (24,25).…”

Vaccine Vectors Harnessing the Power of Cytomegaloviruses

“…CD4 inflation has been much less studied. In a seminal work, a CD4 T cell response specific for the MCMV m09 [133][134][135][136][137][138][139][140][141][142][143][144][145][146][147] peptide was found to be inflationary (although the size of the response was less impressive than those observed in CD8 inflation), indicating that CD4 T cell responses are diverse and may be an interesting target for immunization [117]. This will be expanded on the section dedicated to CD4 T response.…”

“…Out of these determinants, the most intuitive one is gene expression. Operationally, CMV viral transcripts have been divided into three classes [140]. Immediate-early (ie) RNA (identified in the first 6 h post infection), early RNA (synthesized up to about 24 h after infection and required viral transactivators [141]) and late RNA (synthesized after 24 h, requiring viral DNA replication).…”