Host RNA polymerase II (RNA pol-II) is the major enzyme responsible for transcription of mRNA from a DNA template strand. It is made up of 12 subunits Rpb1 to Rpb12. Rpb1 is the largest and catalytical subunit of RNA polymerase II. The carboxy-terminal domain (CTD) of RNA pol-II plays a central role in regulating efficient transcription initiation, elongation and RNA processing. It contains 52 heptapeptide repeats (YSPTSPS) and is phosphorylated largely on Ser-2 and Ser-5 during transcription process.
Some viruses interfere with host RNA pol-II function. They may either mediate its ubiquitination and subsequent proteasomal degradation, or inhibit RNA pol-II phosphorylation thereby lowering its efficiency. Inhibiting host transcription eventually leads to shutoff of host proteins expression and gives viruses transcripts a competitive edge for access to the cellular translation machinery. Preventing the expression of host proteins is also a strategy to counteract the antiviral response.
Viruses inhibiting RNA pol-II:
|Family||Virus||Viral protein||RNA pol-II inhibition strategy||references|
|Herpesviridae||HHV-1||ICP27||RNA pol-II ubiquitination and proteasomal degradation|
|ICP22||Counteracts CTD Ser-2 phosphorylation|
|Bunyaviridae||Bunyamwera virus||NSs||Counteracts CTD Ser-2 phosphorylation|
|Orthomyxoviridae||Influenza virus||Polymerase PB1, PB2, PA||RNA pol-II ubiquitination and proteasomal degradation|
|Togaviridae||Sindbis, Semliki Forest and Chikungunya viruses||nsP2||Ubiquitination of Rpb1 subunit and proteasomal degradation|