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Journal of Virology, October 2005, p. 12721-12731, Vol. 79, No. 20
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.20.12721-12731.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

ADP-Ribose-1"-Monophosphatase: a Conserved Coronavirus Enzyme That Is Dispensable for Viral Replication in Tissue Culture

Ákos Putics,1 Witold Filipowicz,2 Jonathan Hall,3 Alexander E. Gorbalenya,4 and John Ziebuhr1*

Institute of Virology and Immunology, University of Würzburg, Würzburg, Germany,1 Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland,2 Novartis Institutes for Biomedical Research, Basel, Switzerland,3 Molecular Virology Laboratory, Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands4

Received 24 May 2005/ Accepted 20 July 2005

Replication of the ~30-kb plus-strand RNA genome of coronaviruses and synthesis of an extensive set of subgenome-length RNAs are mediated by the replicase-transcriptase, a membrane-bound protein complex containing several cellular proteins and up to 16 viral nonstructural proteins (nsps) with multiple enzymatic activities, including protease, polymerase, helicase, methyltransferase, and RNase activities. To get further insight into the replicase gene-encoded functions, we characterized the coronavirus X domain, which is part of nsp3 and has been predicted to be an ADP-ribose-1"-monophosphate (Appr-1"-p) processing enzyme. Bacterially expressed forms of human coronavirus 229E (HCoV-229E) and severe acute respiratory syndrome-coronavirus X domains were shown to dephosphorylate Appr-1"-p, a side product of cellular tRNA splicing, to ADP-ribose in a highly specific manner. The enzyme had no detectable activity on several other nucleoside phosphates. Guided by the crystal structure of AF1521, an X domain homolog from Archaeoglobus fulgidus, potential active-site residues of the HCoV-229E X domain were targeted by site-directed mutagenesis. The data suggest that the HCoV-229E replicase polyprotein residues, Asn 1302, Asn 1305, His 1310, Gly 1312, and Gly 1313, are part of the enzyme's active site. Characterization of an Appr-1"-pase-deficient HCoV-229E mutant revealed no significant effects on viral RNA synthesis and virus titer, and no reversion to the wild-type sequence was observed when the mutant virus was passaged in cell culture. The apparent dispensability of the conserved X domain activity in vitro indicates that coronavirus replicase polyproteins have evolved to include nonessential functions. The biological significance of the novel enzymatic activity in vivo remains to be investigated.


* Corresponding author. Mailing address: University of Würzburg, Institute of Virology, Versbacher Str. 7, Würzburg 97078, Germany. Phone: 49 931 20149928. Fax: 49 931 20149553. E-mail: j.ziebuhr{at}mail.uni-wuerzburg.de.


Journal of Virology, October 2005, p. 12721-12731, Vol. 79, No. 20
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.20.12721-12731.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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