The Weller lab studies Herpes Simplex Virus type 1, the causative agent of cold sores, ocular infections and debilitating diseases such as encephalitis in immunocompromised individuals. Because it is amenable to genetic and biochemical approaches, HSV serves as an excellent model system for studying the basic mechanisms of the viral life cycle as well virus-host interactions. Experimental approaches used in our laboratory include molecular genetics; confocal microscopy and biochemical, biophysical and structural analysis of viral proteins.
Virus Host Interactions
We are interested in how the virus interacts with the host DNA damage response and cellular protein quality control pathways to create a nuclear environment conducive to viral replication.
Cellular DNA Damage Response Pathways
The cellular DNA damage machinery responds to virus infection and the foreign genomes that accumulate in the nuclei of infected cells. Many DNA viruses have been shown to manipulate the cellular DNA damage response pathways in order to create environments conducive to their own replication. Central transducers of the homologous recombination and non-homologous end joining DNA repair pathways are activated and recruited to viral replication centers while others are inactivated by proteolytic degradation. Current work involves identifying which cellular factors are essential for viral replication and which pathways need to be inactivated for efficient viral infection.
Cellular Protein Quality Control Pathways
Molecular chaperones have long been recognized to play diverse and important roles in the life cycles of many viruses, and we have recently reported that HSV-1 takes advantage of nuclear protein quality control (PQC) mechanisms. During the early stages of HSV infection, Virus-Induced Chaperone-Enriched (VICE) domains form adjacent to nuclear viral replication compartments (RC). VICE domains contain host protein quality control machinery such as molecular chaperones (e.g. Hsc70), the 20S proteasome and ubiquitin which are reorganized from a diffuse nuclear distribution pattern to sequestration in VICE domains. Efficient production of infectious virus requires the activities of Hsc70 and Hsp90. We are actively pursuing the role of the nuclear PQC during HSV-1 infection.
Mechanism of DNA Replication
The cis- and trans-acting elements required for DNA synthesis of Herpes Simplex Virus (HSV) have been identified, and genetic and structural analyses from our lab and others have provided important insights into how they work together to replicate the large double-stranded viral genome. Furthermore, viral enzymes involved in DNA replication have provided a rich store of useful targets for antiviral therapy against herpesviruses. We continue to pursue how the seven viral replication proteins interact with cellular proteins to assemble an active replication fork and establish a replication compartment in the infected nucleus. Approaches include confocal microscopy as well as siRNA depletion of cellular proteins. Another active line of research involves the continued structure-function analysis of viral replication proteins, especially the three-subunit helicase-primase complex UL5/UL8/UL52 and the origin recognition protein UL9. Recent results indicate a novel the mechanism of action of the helicase-primase complex as well as previously unrecognized interactions between UL9 and cellular proteins which may contribute to viral replication.
Many questions remain unresolved concerning the overall mechanism of genome replication. For instance, it has long been recognized that the products of viral DNA replication are head-to-tail concatemers; however, it is not clear how these concatemers are generated. By analogy with the better-studied DNA bacteriophages such as T4 and phage lambda, we and others have suggested that recombination-dependent replication plays a role in viral DNA replication. We propose that viral proteins may function in combination with cellular proteins to produce concatemers suitable for packaging into preformed viral capsids. We have identified a virally encoded recombinase composed of the alkaline nuclease (UL12) and the major single-strand DNA binding protein (ICP8). The viral recombinase interacts with cellular repair/recombination proteins, and we are actively pursuing the roles of each in promoting HSV DNA replication and recombination.
Cleavage and Packaging
Our goal is to gain a better understanding of the capsid assembly and genome cleavage and packaging reactions used by Herpes Simplex Virus type 1 (HSV-1). This complex biological process is likely to involve dynamic interactions between multiple gene products. We have recently discovered that several components of the capsid assembly and encapsidation machinery rely on either viral or host cell chaperones for proper folding and nuclear transport. In addition, our recent studies have implicated disulfide bond formation not only in the assembly of the portal complex but also in several structural proteins in the HSV capsid. We are interested in learning how disulfide bonds form, which proteins are responsible for their formation and how they contribute to overall capsid stability. We have identified a putative viral chaperone involved in the assembly of encapsidation-competent viral capsids which may play a role in disulfide bond formation.