Defective RNA replication by poliovirus mutants deficient in 2A protease cleavage activity.

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2A protease (2Apro) catalyzes the initial cleavage of the poliovirus polyprotein which separates the P1 structural protein precursor from the P2-P3 nonstructural protein precursor. In addition, 2Apro indirectly induces cleavage of the p220 component of eukaryotic initiation factor 4F, which is thought to contribute to the specific inhibition of host cell protein synthesis observed in virus-infected HeLa cells. However, it is unclear whether the trans function of 2Apro which induces host cell shutoff is essential or merely facilitates efficient poliovirus replication. In this study, three point mutations in 2Apro (D38E, Y88L, and Y89L [S. F. Yu and R. E. Lloyd, Virology 182:615-625, 1991]) which cause specific loss of trans but not cis cleavage function were independently introduced into the full-length poliovirus cDNA. In addition, mutations which caused only partial loss of both cis and trans cleavage activities (Y88S) or resulted in a wild-type phenotype (Y88F) were individually introduced. When each of these mutant poliovirus cDNAs was transcribed and translated in vitro, normal proteolytic processing of the viral polyprotein was observed, and p220 was not cleaved in those reactions containing proteases defective in trans function, as expected. Surprisingly, Northern (RNA) blot analysis and reverse transcriptase-PCRs performed after transfection of COS-7 or HeLa cells with these viral RNAs revealed that Y88S and Y88L RNAs replicated at only very low levels. RNA replication could not be detected at all in cells transfected with D38E and Y89L RNAs. Taken together, the results suggest a correlation between the function of 2Apro and productive poliovirus RNA replication in vivo that may be independent of the ability to cause p220 cleavage.

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