Effects of Picornavirus Proteinases on Host Cell Transcription

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Abstract
Poliovirus (PV) is known to shut off both host cell transcription and translation. It is believed that the shutoff of host cell transcription in PV-infected cells increases the pool of free ribonucleotides that the PV-encoded RNA-dependent RNA polymerase (Pol) uses to transcribe and replicate the viral genomic RNA. In support of this theory, PV first shuts off Pol I-mediated transcription in the cell that accounts for greater than 50% of all host cell transcription. The authors have used in vitro transcription systems for understanding the mechanism by which PV shuts off host cell transcription catalyzed by RNA Pol I, II, and III. Infection of susceptible cells with PV results in rapid and dramatic changes in macromolecular metabolism, including the shutoff of host cell transcription. Early attempts to identify the cellular components of the transcriptional machinery inactivated by picornavirus infection focused on the polymerases. To examine whether 3Cpro is sufficient to cause inhibition of host cell transcription seen in virus-infected cells, 3Cpro was cloned into the eukaryotic expression vector pCDNA. The role of the 3C protease in host cell transcription shutoff is clear from both genetic and biochemical analyses. PV is an RNA virus, which replicates in the cytoplasm of infected cells. To shut off host cell transcription, one or more viral gene products must enter the nucleus of the infected host cell. The viral precursor 3CD has protease activity and is able to autocatalyze the formation of 3C and 3D polypeptides.