Viral latency

Viral latency is the ability of a virus to remain dormant within the host cell, sometimes establishing lifelong occult infection. Depending on the virus, the trigger of latency is highly variable but the host cell context is always determining. Latency can stop upon viral genome reactivation, often promoted by stress cellular signals.

The viral genome can remain latent either as an episome or integrated in the host chromosome. The latter allows replication of the viral genome during host cell division. Virus latency is generally maintained by a few viral genes that keep the viral genome silent and escape from host immune system.

Eukaryotic viruses like some herpesviridae or retroviridae are able to infect their host lifelong thanks to latency. This gives them an enormous advantage for disseminating in their host population: about 90% of human population would be infected with varicella-zoster virus.

Virus Family Genus Latent replication form Main site of latency Ref.
Herpesviridae Simplexvirus Circular episome Dorsal root ganglia
HHV-3 Herpesviridae Varicellovirus Circular episome Dorsal root ganglia
HHV-4 Herpesviridae Lymphocryptovirus Circular episome Memory B-cells
HHV-5 Herpesviridae Cytomegalovirus Circular episome Myeloid progenitor cells
HHV-6 Herpesviridae Roseolovirus Probable telomeric integration Monocytes (HHV-6B)
HHV-7 Herpesviridae Roseolovirus Circular episome CD4+ T-cells
HHV-8 Herpesviridae Rhadinovirus Circular episome B-cells
HIV-1 Retroviridae Lentivirus Provirus Memory T-cells
HTLV-1 Retroviridae Deltaretrovirus Provirus Memory T-cells

Prokaryotic viruses which display a latent phase are called “temperate”, or “lysogenic”. The term lysogenic refers to a host phenotype: the bacteria can be spontaneously lysed by the latent phage.
Bacteria such as E. coli and Salmonella contain multiple resident proviruses whose variability in number and type constitutes a major source of diversity between strains . Prokaryotic proviruses usually carry cargo genes encoding traits adaptive to the host, among which are virulence factors found in many bacterial pathogens.

Viruses that have the ability to lie latent within a cell have two options when infecting a cell: they can either enter the latency or the lytic pathway. The decision between lytic and latent pathways is regulated by expression of regulatory proteins part of a genetic switch system, usually repressor(s) as well as proteins controlling the stability of the later. The outcome of the followed pathways depends on the ratio of these key regulators. This ratio may be determined by environmental factors such as the host cell type, its shape, or the nutriment availability.
A well known genetic switch system is the one of bacteriophage lambda which includes at least a repressor of the lytic promoter, a repressor of the latency promotor and two key regulators .

Matching UniProtKB/Swiss-Prot entries

10 entries grouped by strain (browse by keywords)

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2 entries

Bacillus phage SPbeta (Bacillus phage SPBc2) (Bacteriophage SP-beta) reference strain

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AIMP_BPSPBProtein AimP (YopL protein)
AIMR_BPSPBAimR transcriptional regulator (Arbitrium communication peptide receptor) (YopK ...

2 entries

Escherichia phage Mu (Bacteriophage Mu) reference strain

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GEMA_BPMUGemA protein (Gene product 16) (gp16)
REPC_BPMURepressor protein c (Repc) (CI) (Gene product 1) (gp1) (Mu repressor) (MuR)

2 entries

Escherichia phage lambda (Bacteriophage lambda) reference strain

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RCRO_LAMBDRegulatory protein cro
RPC1_LAMBDRepressor protein cI

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Bacillus phage phi3T (Bacteriophage phi-3T)

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AIMR_BPPHTAimR transcriptional regulator (Arbitrium communication peptide receptor)

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Escherichia phage D108 (Bacteriophage D108)

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GEMA_BPD10GemA protein (Gene product 16) (gp16)
REPC_BPD10Repressor c protein (Repc) (CI)