IN VITRO STUDIES TO ELUCIDATE THE BIOCHEMICAL FUNCTIONS OF EPSTEIN-BARR VIRUS TEGUMENT PROTEIN BKRF4

Author

PRIYA PADMANABHAN THAIVALAPPIL, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2011

Degree Name

Master of Science

Department

Molecular Biology Microbiology and Biochemistry

First Advisor

Gershburg, Edward

Abstract

Epstein Barr Virus (EBV) is an opportunistic pathogen that causes infectious mononucleosis and associated with Burkitt's lymphoma, nasopharyngeal carcinoma and lymphoproliferative diseases. Throughout the life cycle, EBV genomes attain different levels of chromatinization, transitioning from a fully chromatinized form, which mimics cellular chromatin during latency, through an intermediately chromatinized form during the lytic phase, to a completely non-chromatinized DNA when packaged into the virions. Chromatinization dynamics in vivo requires the coordinated action of multiple proteins including histone chaperones, which are responsible for histone transport, deposition and exchange. Previous studies show that viruses often exploit cellular histone chaperones; however, no virally-encoded histone chaperone has been identified to date. Studies presented here, describe in vitro activities of the EBV tegument protein BKRF4, and suggest that it might represent the first bona-fide viral histone chaperone. This is based on the following observations: (1) BKRF4 protein contains acidic domains, negatively charged clusters that are involved in interaction with histones and neutralization of their positive charge; (2) purified BKRF4 protein interacts with core histone octamers in vitro, preferentially binding H2B, H3 and H4; (3) BKRF4 facilitates the dissociation of DNA from core histones in vitro similar to cellular histone chaperones; (4) immunofluorescence staining and biochemical fractionation experiments demonstrate that BKRF4 protein localizes in the nucleus, predominantly, in the chromatin fraction along with histones. These data indicate that BKRF4 might contribute to the chromatinization dynamics of the EBV genomes, in particular at the step of DNA packaging that requires removal of remaining histones. Further studies are warranted to verify our in vitro data in the context of viral infection in order to extend our understanding of the mechanisms and significance of herpesvirus genome chromatinization and virus-host chromatin interactions.