Characterization of the Kaposi's sarcoma-associated herpesvirus terminase complex component ORF29

Area of Science:

• Virology
• Molecular Biology
• Infectious Diseases

Background:

• Kaposi's sarcoma-associated herpesvirus (KSHV) is a human oncogenic virus belonging to the Gammaherpesvirinae subfamily.
• Viral capsid formation and genome packaging occur during the lytic phase, involving the terminase complex.
• The KSHV terminase complex, crucial for DNA cleavage and packaging, is poorly understood, with ORF7, ORF67.5, and ORF29 as putative components.

Purpose of the Study:

• To elucidate the role of KSHV ORF29 in viral replication and terminase complex function.
• To investigate the impact of ORF29 deficiency on KSHV capsid formation, DNA cleavage, and virion production.

Main Methods:

• Construction and analysis of an ORF29-deficient KSHV mutant.
• Assessment of viral properties including virion production, terminal repeat (TR) cleavage, and capsid morphology.
• Investigation of protein-protein interactions among KSHV terminase components (ORF7, ORF67.5, ORF29).

Main Results:

• ORF29 is essential for KSHV virion production and TR cleavage.
• Cells with ORF29-deficient KSHV exhibit numerous immature, soccer ball-like capsids.
• ORF29 self-interacts and is required for terminase complex assembly, with its N-terminal region mediating interaction with ORF7.

Conclusions:

• ORF29 is a fundamental component of the KSHV terminase complex, critical for mature capsid formation and DNA processing.
• ORF29's self-interaction may facilitate terminase complex multimerization or ring formation, analogous to herpes simplex virus 1.
• Understanding ORF29 function provides insights into KSHV DNA packaging and potential therapeutic targets.