Evidence for G-quadruplex-mediated transactivation by the immediate-early 2 protein of human cytomegalovirus

G4-quadruplex (G4) is a noncanonical nucleic acid secondary structure that forms in single-stranded DNA or RNA. G4 structures are involved in various cellular processes, including transcription, translation, and DNA replication. It has been shown that G4 formation in gene promoters can inhibit promoter activation. Recently, a positive role of G4 in promoters has also been discovered, but evidence in viral promoters remains limited. In this study, we demonstrate that a G4 structure forms in the human cytomegalovirus UL146 promoter and acts as a binding site for the viral transactivator IE2, which plays a key role in viral gene expression. Using recombinant viruses, we confirm that IE2 binding to G4 is necessary for efficient UL146 transcription during virus infection. This study provides evidence that G4 structures in promoters can positively regulate viral gene expression and uncovers a novel mechanism by which IE2 activates gene expression.