2017 Theses Doctoral

Biochemical and Genetic Investigation of Immature Murine Leukemia Virus Assembly

Tinaztepe, Sedef

Production of infectious retrovirus particles is a complex and poorly-understood process with multiple steps that are often linked to one another. Our aim in this study was to gain better understanding of the path the murine leukemia virus (MLV) structural protein Gag follows to assemble into immature capsid structures, the process of which is central to retroviral assembly and release. Extensive studies of human immunodeficiency virus type 1 (HIV-1) assembly have led to the development of a model proposing that the assembly of immature HIV-1 capsids proceeds sequentially through multiple intermediates, in association with an RNA granule containing some well-conserved cellular factors, such as ATP-binding cassette subfamily E member 1 (ABCE1) and DEAD-box helicase 6 (DDX6). In this work, we provided evidence suggesting that MLV Gag associates with endogenous ABCE1 in human cells expressing assembly-competent MLV, and can be found in at least three high-molecular weight complexes with sedimentation properties highly resembling the HIV-1 assembly intermediates. Furthermore, we assessed the Gag proteins of select assembly-defective MLV mutants in terms of their expression levels, ability to form viral particles, involvement in intracellular complexes, membrane association, and ABCE1 interaction. Our findings were not only consistent with a model of MLV assembly through host-mediated intermediates, but also provided novel information about the effects of various MLV Gag mutations that are associated with defects in particle production.