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Journal of Virology, December 2009, p. 12118-12128, Vol. 83, No. 23
0022-538X/09/$08.00+0     doi:10.1128/JVI.01336-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Minimum Replication Origin of Merkel Cell Polyomavirus Has a Unique Large T-Antigen Loading Architecture and Requires Small T-Antigen Expression for Optimal Replication{triangledown} ,{ddagger}

Hyun Jin Kwun,1 Anna Guastafierro,1 Masahiro Shuda,1 Gretchen Meinke,2 Andrew Bohm,2 Patrick S. Moore,1,{dagger}* and Yuan Chang1,{dagger}*

Molecular Virology Program, University of Pittsburgh Cancer Institute, University of Pittsburgh, 5117 Centre Avenue, Pittsburgh, Pennsylvania 15213,1 Department of Biochemistry, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, Massachusetts 021112

Received 29 June 2009/ Accepted 8 September 2009

Merkel cell polyomavirus (MCV) is a recently discovered human polyomavirus causing the majority of human Merkel cell carcinomas. We mapped a 71-bp minimal MCV replication core origin sufficient for initiating eukaryotic DNA replication in the presence of wild-type MCV large T protein (LT). The origin includes a poly(T)-rich tract and eight variably oriented, GAGGC-like pentanucleotide sequences (PS) that serve as LT recognition sites. Mutation analysis shows that only four of the eight PS are required for origin replication. A single point mutation in one origin PS from a naturally occurring, tumor-derived virus reduces LT assembly on the origin and eliminates viral DNA replication. Tumor-derived LT having mutations truncating either the origin-binding domain or the helicase domain also prevent LT-origin assembly. Optimal MCV replication requires coexpression of MCV small T protein (sT), together with LT. An intact DnaJ domain on the LT is required for replication but is dispensable on the sT. In contrast, PP2A targeting by sT is required for enhanced replication. The MCV origin provides a novel model for eukaryotic replication from a defined DNA element and illustrates the selective pressure within tumors to abrogate independent MCV replication.

* Corresponding authors. Mailing address: University of Pittsburgh Cancer Institute, 5117 Centre Ave., Ste. 1.8, Pittsburgh, PA 15213. Phone: (412) 623-7721. Fax: (412) 623-7715. E-mail for Y. Chang: yc70{at}pitt.edu. E-mail for P. S. Moore: psm9{at}pitt.edu

{triangledown} Published ahead of print on 16 September 2009.

{ddagger} Supplemental material for this article may be found at http://jvi.asm.org/.

{dagger} P.S.M. and Y.S. contributed equally to this study.

Journal of Virology, December 2009, p. 12118-12128, Vol. 83, No. 23
0022-538X/09/$08.00+0     doi:10.1128/JVI.01336-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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