This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Agarkova, I. V. Articles by Van Etten, J. L. Search for Related Content PubMed PubMed Citation Articles by Agarkova, I. V. Articles by Van Etten, J. L.

 Previous Article  |  Next Article 

Journal of Virology, August 2006, p. 8114-8123, Vol. 80, No. 16
0022-538X/06/$08.00+0     doi:10.1128/JVI.00486-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Virion-Associated Restriction Endonucleases of Chloroviruses

Irina V. Agarkova, David D. Dunigan, and James L. Van Etten^*

Department of Plant Pathology and Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska 68583-0722

Received 8 March 2006/ Accepted 26 May 2006

Chloroviruses are large, double-stranded-DNA, plaque-forming viruses that infect certain eukaryotic chlorella-like green algae. The prototype of the genus is Paramecium bursaria chlorella virus 1 (PBCV-1). Chlorovirus genomes contain various amounts of methylated nucleotides due to virus-encoded DNA methyltransferases (MTases); about 25% of the MTases are associated with companion DNA site-specific (restriction) endonucleases (REases). These enzymes constitute virally encoded restriction-modification (R/M) systems. Although several of the chlorovirus R/M systems are characterized, their biological functions are unknown. The PBCV-1 proteome reveals that two virus-encoded REases, but not their companion MTases, are virion associated, suggesting that viral REases might help degrade the host DNA early in infection. To test this hypothesis, host chromosomal DNA from PBCV-1-infected cells was examined by pulsed-field gel electrophoresis. Initiation of host chromosomal DNA degradation occurred within 5 min postinfection (p.i.). The DNA degradation was insensitive to protein synthesis inhibitors or UV inactivation of virus particles, consistent with the agent being a small protein associated with the virion. Nuclease activities, including those of the two predicted REases and an uncharacterized general nuclease(s), were detected in disrupted PBCV-1 particles. The general nuclease(s) degraded both host and viral DNAs in vitro, although the viral DNA was not degraded in vivo, suggesting differential intracellular trafficking of the virion-associated nucleases. Infection with chloroviruses lacking an R/M system(s) resulted in either delayed host chromosomal DNA degradation or no detectable host chromatin changes. These immediate-early events associated with chlorovirus infections may facilitate rapid switching of the host transcriptional apparatus to viral transcription, which begins within 5 to 10 min p.i.

---

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

---

Journal of Virology, August 2006, p. 8114-8123, Vol. 80, No. 16
0022-538X/06/$08.00+0     doi:10.1128/JVI.00486-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Ishikawa, K., Handa, N., Kobayashi, I. (2009). Cleavage of a model DNA replication fork by a Type I restriction endonuclease. Nucleic Acids Res 37: 3531-3544 [Abstract] [Full Text]  
• Agarkova, I., Dunigan, D., Gurnon, J., Greiner, T., Barres, J., Thiel, G., Van Etten, J. L. (2008). Chlorovirus-Mediated Membrane Depolarization of Chlorella Alters Secondary Active Transport of Solutes. J. Virol. 82: 12181-12190 [Abstract] [Full Text]