Recombinant Human herpesvirus 1 mRNA export factor (UL54), partial

Multifunctional regulator of the expression of viral genes that contributes to the shutoff of host protein synthesis and mediates nuclear export of viral intronless mRNAs. Early in infection, this immediate early (EI) protein mediates the inhibition of cellular splicing. This results in the accumulation of unprocessed 3'end pre-mRNAs which can't be exported from the nucleus. Cellular protein synthesis is thereby shut off early after virus infection. Later in the infection, it helps recruit cellular RNA polymerase II to viral replication sites and promotes the nuclear export of viral intronless mRNAs by interacting with mRNAs and host NXF1/TAP. ICP27 binds to NUP62 which may provide facilitated viral mRNA export and may indirectly compete with some host cell transport receptors for binding and inhibit cellular nucleocytoplasmic transport pathways. Also stimulates translation of viral transcripts. Repression of host gene expression blocks the cell cycle at the G1 phase and prevents apoptosis. Seems to silence the 3' splice site of the promyelocytic leukemia (PML) intron 7a, thereby switching PML isoforms from PML-II to PML-V. This could be linked to the accelerated mRNA export induced by ICP27 which might not provide sufficient time for PML pre-mRNA to be spliced in the nucleus.