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. Also stimulates translation of viral transcripts (PubMed:25540385). Independently, plays a role in the regulation of virion release (PubMed:25540385). Also plays a role in the inhibition of host innate immune response by targeting host IRF3 and therby preventing production of beta-interferon (PubMed:30863402). Silences the 3' splice site of the host 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 (PubMed:19729513). Suppresses also splicing of the viral ICP34.5 mRNA, allowing the virus to express a variant form of ICP34.5 (PubMed:23487469). Interacts with host RBP1; this interaction facilitates the RNA polymerase recruitment to viral transcription sites. Interacts (via the RGG box) with host ALYREF/THOC4; this interaction recruits ALYREF to viral replication compartments and probably directs viral mRNA to the TAP/NFX1 pathway. Interacts (via the RGG box) with host SRPK1; this interaction relocalizes SRPK1 to the nucleus and seems to alter its activity. Interacts with ICP4; this interaction modulates ICP4 DNA-binding activity. Interacts with host NXF1; this interaction allows efficient export of HSV-1 early and late transcripts (By similarity). Interacts with host IRF3; this interaction inhibits IRF3 phosphorylation and nuclear translocation. Shuttles between the nucleus and the cytoplasm. Binds viral intronless RNAs through the RGG region. The N-terminal domain is mainly responsible for the inhibition of IFN-beta induction. Methylated within the RGG box possibly by host PRMT1. When hypomethylated, ICP27 is exported to the cytoplasm earlier and more rapidly (By similarity). Phosphorylated. Belongs to the HHV-1 ICP27 protein family.