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Journal of Virology, July 2007, p. 7662-7671, Vol. 81, No. 14
0022-538X/07/$08.00+0     doi:10.1128/JVI.00186-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Chloroviruses Encode a Bifunctional dCMP-dCTP Deaminase That Produces Two Key Intermediates in dTTP Formation{triangledown}

Yuanzheng Zhang,1,§ Frank Maley,2 Gladys F. Maley,2 Garry Duncan,3 David D. Dunigan,1,4 and James L. Van Etten1,4*

Department of Plant Pathology, University of Nebraska—Lincoln, Lincoln, Nebraska 68583-0722,1 Wadsworth Center, New York State Department of Health, Albany, New York 12201-0509,2 Department of Biology, Nebraska Wesleyan University, Lincoln, Nebraska 68504-2794,3 Nebraska Center of Virology, University of Nebraska—Lincoln, Lincoln, Nebraska 68588-06664

Received 26 January 2007/ Accepted 26 April 2007

The chlorovirus PBCV-1, like many large double-stranded DNA-containing viruses, contains several genes that encode putative proteins involved in nucleotide biosynthesis. This report describes the characterization of the PBCV-1 dCMP deaminase, which produces dUMP, a key intermediate in the synthesis of dTTP. As predicted, the recombinant protein has dCMP deaminase activity that is activated by dCTP and inhibited by dTTP. Unexpectedly, however, the viral enzyme also has dCTP deaminase activity, producing dUTP. Typically, these two reactions are catalyzed by proteins in separate enzyme classes; to our knowledge, this is the first example of a protein having both deaminase activities. Kinetic experiments established that (i) the PBCV-1 enzyme has a higher affinity for dCTP than for dCMP, (ii) dCTP serves as a positive heterotropic effector for the dCMP deaminase activity and a positive homotropic effector for the dCTP deaminase activity, and (iii) the enzymatic efficiency of the dCMP deaminase activity is about four times higher than that of the dCTP deaminase activity. Inhibitor studies suggest that the same active site is involved in both dCMP and dCTP deaminations. The discovery that the PBCV-1 dCMP deaminase has two activities, together with a previous report that the virus also encodes a functional dUTP triphosphatase (Y. Zhang, H. Moriyama, K. Homma, and J. L. Van Etten, J. Virol. 79:9945-9953, 2005), means that PBCV-1 is the first virus to encode enzymes involved in all three known pathways to form dUMP.

* Corresponding author. Mailing address: Department of Plant Pathology, University of Nebraska—Lincoln, Lincoln, NE 68583-0722. Phone: (402) 472-3168. Fax: (402) 472-2853. E-mail: jvanetten{at}unlnotes.unl.edu

{triangledown} Published ahead of print on 2 May 2007.

§ Present address: Schering-Plough Animal Health Corporation, Elkhorn, NE 68022.

Journal of Virology, July 2007, p. 7662-7671, Vol. 81, No. 14
0022-538X/07/$08.00+0     doi:10.1128/JVI.00186-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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