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UBC Theses and Dissertations

Characterization of the cricket paralysis virus 3C protease and its substrate specificity Brito, Ruhi Nichalle


Many positive-sense single-stranded RNA (+ssRNA) viruses encode an open reading frame that is translated as a polyprotein. This viral polyprotein is subsequently cleaved by its virally encoded protease or in some instances with the aid of host proteases. It has been well established that +ssRNA viruses, such as poliovirus encode protease(s) that can cleave and target host protein substrates in order to facilitate viral infection. The Dicistrovirade family, are +ssRNA viruses that primarily infect arthropods such as honey bees, shrimp, and crickets and can have an impact on agriculture and the economy. Dicistroviruses encode a cysteine protease, 3C, that is responsible for the cleavage of its own polyprotein. To date little is known about dicistrovirus protease structure, catalytic efficiency, cleavage site specificity and substrate specificity. Cricket paralysis virus (CrPV), a dicistrovirus, has been well characterized within its family. CrPV has been characterized for its translation mechanism as well as a few of its encoded proteins such as 1A, thus making it a good model to study. Given that other +ssRNA viral 3C proteases, such as poliovirus, cleave host substrates during infection, it could be thought that the CrPV 3C protease cleaves target host proteins during infection. In order to better understand the fundamental processes that are regulated during infection, CrPV was chosen as a model. In this thesis CrPV 3C protease was purified to address two aims. 1) Purify and verify activity of CrPV 3C protease and 2) Determine cleavage site specificity of CrPV 3C protease. This will help give a better understanding of the catalytic efficiency and target substrate specificity of the purified protease.

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