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Journal of Virology, March 2009, p. 2708-2714, Vol. 83, No. 6
0022-538X/09/$08.00+0     doi:10.1128/JVI.01610-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

P64, a Novel Major Virion DNA-Binding Protein Potentially Involved in Condensing the Spodoptera frugiperda Ascovirus 1a Genome{triangledown}

Yeping Tan,1,{dagger} Tatsinda Spears,1,{dagger} Dennis K. Bideshi,1,2,{dagger} Jeffrey J. Johnson,1 Robert Hice,1 Yves Bigot,3 and Brian A. Federici1,4*

Department of Entomology, University of California—Riverside, Riverside, California 92521,1 California Baptist University, Department of Natural and Mathematical Sciences, 8432 Magnolia Avenue, Riverside, California 92504,2 Laboratoire d'Estude des Parasites Genetiques, Universite Francois Rabelais, UFR Sciences et Techniques, 37200 Tours, France,3 Interdepartmental Graduate Programs in Genetics and Cell, Molecular & Developmental Biology, University of California—Riverside, Riverside, California 925214

Received 29 July 2008/ Accepted 2 January 2009

We recently identified 21 structural proteins in the virion of Spodoptera frugiperda ascovirus 1a (SfAV1a), a virus with a large, double-stranded DNA genome of 157 kbp, which attacks species of the lepidopteran family Noctuidae. The two most abundant virion proteins were the major capsid protein and a novel protein (P64) of 64 kDa that contained two distinct domains not known previously to occur together. The amino-terminal half of P64 (residues 1 to 263) contained four repeats (a recently recognized motif with an unknown function) of a virus-specific two-cysteine adaptor. Adjoined to this, the carboxy-terminal half of P64 (residues 279 to 455) contained 14 copies of a highly basic, tandemly repeated motif rich in arginine and serine, having an 11- to 13-amino-acid consensus sequence, SPSQRRSTS(V/K)(A/S)RR, yielding a predicted isoelectric point of 12.2 for this protein. In the present study, we demonstrate by Southwestern analysis that SfAV1a P64 was the only virion structural protein that bound DNA. Additional electrophoretic mobility shift assays showed that P64 bound SfAV1a as well as non-SfAV1a DNA. Furthermore, we show through immunogold labeling of ultrathin sections that P64 is a component of virogenic stroma and appears to be progressively incorporated into the SfAV1a DNA core during virion assembly. As no other virion structural protein bound DNA and no basic DNA-binding proteins of lower mass are encoded by the SfAV1a genome or were identified by proteomic analysis, our results suggest that P64's function is to condense the large genome of this virus and assist in packaging this genome into its virion.

* Corresponding author. Mailing address: Department of Entomology, University of California—Riverside, Riverside, CA 92521. Phone: (951) 827-5006. Fax: (951) 827-3086. E-mail: brian.federici{at}ucr.edu

{triangledown} Published ahead of print on 7 January 2009.

{dagger} Y.T,. T.S., and D.K.B. contributed equally to this work.

Journal of Virology, March 2009, p. 2708-2714, Vol. 83, No. 6
0022-538X/09/$08.00+0     doi:10.1128/JVI.01610-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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