| HHV‑8 K‑bZIP (also termed K8) is a basic region–leucine zipper transcriptional regulator encoded by the lytic K8 open reading frame of Kaposi’s sarcoma–associated herpesvirus that functions as a nuclear DNA‑binding protein and protein–protein interaction hub controlling the balance between latency and lytic replication and modulating viral and host transcription programs in infected cells. The protein contains an N‑terminal basic region that confers sequence‑specific DNA binding and a C‑terminal leucine zipper that mediates stable homodimer formation and interaction with other transcriptional regulators, and extensive splicing of the K8 transcript produces the K‑bZIP isoform that localizes to the nucleus and associates with viral promoters and regulatory protein complexes. K‑bZIP directly binds the immediate‑early transactivator Rta (ORF50) through its leucine zipper domain and represses Rta‑mediated transactivation of the K8 promoter and other Rta‑responsive promoters, establishing a negative‑feedback circuit that limits Rta activity and shapes the temporal pattern of early lytic gene expression and viral reactivation from latency. K‑bZIP also functions as an E3 SUMO ligase that recruits the SUMO conjugation machinery to itself and to chromatin‑associated complexes and promotes SUMO modification of transcription factors and of histone H3 at low‑methylated Lys9 regions on viral promoters, thereby generating repressive chromatin and reducing transcription from selected viral and cellular genes while leaving other loci accessible for activation by Rta and host cofactors. Interaction of K‑bZIP with histone deacetylases and with latency‑associated nuclear antigen (LANA) links this protein to broader epigenetic control of the HHV‑8 episome, where K‑bZIP modulates LANA‑mediated repression at lytic origins of replication and participates in switching between latent maintenance and lytic DNA replication. K‑bZIP is required for full lytic viral gene expression, DNA replication, and production of infectious virions, placing this factor as an essential component of the lytic transcriptional machinery and as a key determinant of viral propagation in HHV‑8–associated lymphomas and Kaposi’s sarcoma lesions. |
Lane 1: HHV-8 K-bZIP recombinant protein
