Human cytomegalovirus immediate-early protein 2 (IE2) (IE2 (also IE2-86 for the 86-kDa form))

Human cytomegalovirus IE2 is the major immediate-early regulatory protein encoded by UL122; the functionally active form is an approximately 80–86 kDa nuclear protein produced from transcripts that splice exons 2–3 to exon 5, with exon 5 encoding the distinct C‑terminal regulatory domains.[1][5] IE2 is indispensable for viral early gene expression and acts as a DNA sequence‑specific binding protein that can both repress and activate transcription, including autorepression at the major immediate-early promoter through the cis‑repression sequence and recruitment of histone deacetylases.[6][5] IE2 interacts with numerous cellular transcriptional regulators (AP-1, CREB1, EGR1, SP1, p53, Rb, TAF4, TBP, TFIIB, TFIID), chromatin assembly and modifying factors (CAF-1, HATs, HDACs), and modulates chromatin acetylation states during infection.[6][5] It coordinates with UL84 at OriLyt and regulates the OriLyt RNA4.9 promoter, which functions as a strong enhancer important for viral DNA replication; specific IE2 variants (e.g., H388D) can compensate for lack of UL84 in certain strains, highlighting strain-dependent replication mechanisms.[3][6] Beyond transcriptional control, IE2 contributes to immune evasion and anti-apoptotic effects during early infection, supporting productive replication.[4] Notes on nomenclature and structure: - “Exon 5” denotes the exon encoding the unique C‑terminal portion of IE2; multiple overlapping polypeptides from exon 5 were described, but only the 80‑kDa full-length IE2 containing exons 2–3 plus intact exon 5 showed full transactivation and autoregulatory activity, with essential activation domains mapped within both N‑terminal and C‑terminal (exon 5) regions.[1]

Other names

Immediate-early 2 proteinIE2-86UL122 gene productHCMV IE2Major immediate-early 2 protein

For putative IE2-targeting strategies (research concepts): inhibition of IE2 DNA-binding or cofactor interactions; disruption of IE2–HDAC/HAT interfaces; blockade of IE2 recruitment to OriLyt/RNA4.9 enhancer. These are mechanistic inferences based on IE2 biology, not established drug MoAs.