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Journal of Virology, July 2009, p. 6934-6940, Vol. 83, No. 13
0022-538X/09/$08.00+0     doi:10.1128/JVI.00537-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cassava Brown Streak Virus (Potyviridae) Encodes a Putative Maf/HAM1 Pyrophosphatase Implicated in Reduction of Mutations and a P1 Proteinase That Suppresses RNA Silencing but Contains No HC-Pro {triangledown}

Deusdedith R. Mbanzibwa,1,2,3,{dagger} Yanping Tian,1,{dagger} Settumba B. Mukasa,2 and Jari P. T. Valkonen1*

Department of Applied Biology, University of Helsinki, P.O. Box 27, Helsinki FIN-00014, Finland,1 Department of Crop Science, Makerere University, P.O. Box 7062, Kampala, Uganda,2 Mikocheni Agricultural Research Institute, P.O. Box 6226, Dar es Salaam, Tanzania3

Received 16 March 2009/ Accepted 15 April 2009

The complete positive-sense single-stranded RNA genome of Cassava brown streak virus (CBSV; genus Ipomovirus; Potyviridae) was found to consist of 9,069 nucleotides and predicted to produce a polyprotein of 2,902 amino acids. It was lacking helper-component proteinase but contained a single P1 serine proteinase that strongly suppressed RNA silencing. Besides the exceptional structure of the 5'-proximal part of the genome, CBSV also contained a Maf/HAM1-like sequence (678 nucleotides, 226 amino acids) recombined between the replicase and coat protein domains in the 3'-proximal part of the genome, which is highly conserved in Potyviridae. HAM1 was flanked by consensus proteolytic cleavage sites for ipomovirus NIaPro cysteine proteinase. Homology of CBSV HAM1 with cellular Maf/HAM1 pyrophosphatases suggests that it may intercept noncanonical nucleoside triphosphates to reduce mutagenesis of viral RNA.

* Corresponding author. Mailing address: Department of Applied Biology, University of Helsinki, P.O. Box 27, Helsinki FIN-00014, Finland. Phone: 358-9-19158387. Fax: 358-9-19158727. E-mail: jari.valkonen{at}helsinki.fi

{triangledown} Published ahead of print on 22 April 2009.

{dagger} The first two authors contributed equally.

Journal of Virology, July 2009, p. 6934-6940, Vol. 83, No. 13
0022-538X/09/$08.00+0     doi:10.1128/JVI.00537-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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