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EMBO J. 1994 Jun 15;13(12):2925-34.

Polypeptide requirements for assembly of functional Sindbis virus replication complexes: a model for the temporal regulation of minus- and plus-strand RNA synthesis.

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Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110-1093.


Proteolytic processing of the Sindbis virus non-structural polyproteins (P123 and P1234) and synthesis of minus- and plus-strand RNAs are highly regulated during virus infection. Although their precise roles have not been defined, these polyproteins, processing intermediates or mature cleavage products (nsP1-4) are believed to be essential components of viral replication and transcription complexes. In this study, we have shown that nsP4 can function as the polymerase for both minus- and plus-strand RNA synthesis. Mutations inactivating the nsP2 proteinase, resulting in uncleaved P123, led to enhanced accumulation of minus-strand RNAs and reduced accumulation of genomic and subgenomic plus-strand RNAs. In contrast, no RNA synthesis was observed with a mutation which increased the efficiency of P123 processing. Inclusion of this mutation in a P123 polyprotein with cleavage sites 1/2 and 2/3 blocked allowed synthesis of both minus- and plus-strand RNAs. We conclude that nsP4 and uncleaved P123 normally function as the minus-strand replication complex, and propose that processing of P123 switches the template preference of the complex to minus-strands, resulting in efficient synthesis of plus-strand genomic and subgenomic RNAs and shut-off of minus-strand RNA synthesis.

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