Gary Blissard

Because they represent a highly host-specific and thus environmentally friendly alternative to chemical methods of insect control, baculoviruses will likely comprise an important component of future strategies for biological control in both agriculture and forestry. Baculoviruses have also been developed and used extensively in research, serving as invaluable expression vectors for high level production of recombinant proteins. In addition, baculoviruses serve as convenient model systems for studies of virus entry and exit, transcriptional regulation, DNA replication, and other host-pathogen interactions.

Viral entry and exit. To enter a host cell, the envelope of the baculovirus must fuse with the host plasma membrane, releasing the nucleocapsid (which carries the viral genome) into the cell. Membrane fusion occurs at a low pH, during a process known as receptor-mediated endocytosis. In early studies, we found that a viral envelope glycoprotein known as GP64, was necessary and sufficient for the low pH-activated membrane fusion activity that occurs during endocytosis. We also demonstrated that the GP64 protein serves as a viral attachment protein at the cell surface (at the first step of cellular entry). Our studies also showed that the GP64 protein is involved in virus assembly during the final phase of the infection cycle, when progeny virus particles bud from the cell surface. Current studies are focused on understanding how the structure and organization of this important protein facilitate these diverse and essential functions. For these studies, we are using a variety of physical, biochemical, genetic, and molecular techniques to identify and define specific functional domains of the GP64 protein. Of particular importance, we recently developed a GP64 knockout virus, and a system for replacing the essential wild type gp64 gene with mutant forms of gp64. These powerful molecular tools are allowing us to perform detailed studies of the roles of this envelope protein, and the functions of specific protein domains - all in the context of the viral infection, as well as with infected host animals (insects).

Viral gene expression. We are also examining the regulation of baculovirus gene expression. The large genomes of baculoviruses may encode over 150 genes and these genes are expressed in two major phases, early and late. Early phase genes are transcribed by the host cell’s RNA polymerase II, whereas late phase genes are transcribed by a viral encoded have focused on the identification of sequences regulating early and late viral transcription, and on host and viral regulatory proteins that interact with viral regulatory sequences. We are currently using a genetic knockout system to examine the roles of specific late expression factor (LEF) genes in regulating late gene transcription. A major goal of these studies is to more broadly understand the regulation of viral gene expression and to develop regulatory paradigms within this virus family. By studying DNA sequence motifs and the host and viral proteins required for the activation and modulation of baculovirus gene expression, we are developing a better understanding of the intricate mechanisms regulating gene expression from these large viral genomes.

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