L. J. Marshall, L. Dunham and E. O. Major efficiency. Immunofluorescence was performed on day 6 post- nucleofection to measure T-antigen expression in GFAP-positive PDAs. Generation of figures. Digital Western blot images were detected using fluorescent filters in a FluorChem Q imager (Alpha Innotech). Digital EMSA images were obtained by scanning the exposed film using an hp Scanjet 8250 (Hewlett Packard Development Company). Figures were generated using Canvas II (ACD Systems International Inc.) and Adobe photoshop CS2 (Adobe). ACKNOWLEDGEMENTS We thank Franc¸oise Moreau-Gachelin of the Institut Curie (Paris, France) for generously providing the Spi-B antiserum and human Spi-B plasmid. We thank Ludwig Kappos and Raija Lindberg at the University of Basel (Basel, Switzerland) for their valuable discussions during this work. We thank all of the members of the Laboratory of Molecular Medicine and Neuroscience at the NINDS for all of their hard work, support and invaluable input during this work. REFERENCES Amemiya, K., Traub, R., Durham, L. & Major, E. O. (1989). Interaction of a nuclear factor-1-like protein with the regulatory region of the human polyomavirus JC virus. J Biol Chem 264, 7025–7032. Amemiya, K., Traub, R., Durham, L. & Major, E. O. (1992). Adjacent nuclear factor-1 and activator protein binding sites in the enhancer of the neurotropic JC virus. A common characteristic of many brain- specific genes. J Biol Chem 267, 14204–14211. Andrews, N. C. & Faller, D. V. (1991). A rapid micropreparation technique for extraction of DNA-binding proteins from limiting numbers of mammalian cells. Nucleic Acids Res 19, 2499. Araki, K., Maeda, H., Wang, J., Kitamura, D. & Watanabe, T. (1988). Purification of a nuclear trans-acting factor involved in the regulated transcription of a human immunoglobulin heavy chain gene. Cell 53, 723–730. Arguello, M., Sgarbanti, M., Hernandez, E., Mamane, Y., Sharma, S., Servant, M., Lin, R. & Hiscott, J. (2003). Disruption of the B-cell specific transcriptional program in HHV-8 associated primary effusion lymphoma cell lines. Oncogene 22, 964–973. Ault, G. S. & Stoner, G. L. (1993). Human polyomavirus JC promoter/ enhancer rearrangement patterns from progressive multifocal leu- koencephalopathy brain are unique derivatives of a single archetypal structure. J Gen Virol 74, 1499–1507. Bartholdy, B., Du Roure, C., Bordon, A., Emslie, D., Corcoran, L. M. & Matthias, P. (2006). The Ets factor Spi-B is a direct critical target of the coactivator OBF-1. Proc Natl Acad Sci U S A 103, 11665–11670. Biosystems, A. (2008). Guide to Performing Relative Quantitation of Gene Expression Using Real-Time Quantitative PCR, pp. 44–51. Technical Note. Foster City: Applied Biosystems. Chang, C. F., Gallia, G. L., Muralidharan, V., Chen, N. N., Zoltick, P., Johnson, E. & Khalili, K. (1996). Evidence that replication of human neurotropic JC virus DNA in glial cells is regulated by the sequence- specific single-stranded DNA-binding protein Pur a. J Virol 70, 4150– 4156. Chen, N. N. & Khalili, K. (1995). Transcriptional regulation of human JC polyomavirus promoters by cellular proteins YB-1 and Pur a in glial cells. J Virol 69, 5843–5848. Chen, H., Ray-Gallet, D., Zhang, P., Hetherington, C. J., Gonzalez, D. A., Zhang, D. E., Moreau-Gachelin, F. & Tenen, D. G. (1995a). 3050 PU.1 (Spi-1) autoregulates its expression in myeloid cells. Oncogene 11, 1549–1560. Chen, H. M., Zhang, P., Voso, M. T., Hohaus, S., Gonzalez, D. A., Glass, C. K., Zhang, D. E. & Tenen, D. G. (1995b). Neutrophils and monocytes express high levels of PU.1 (Spi-1) but not Spi-B. Blood 85, 2918–2928. Chen, N. N., Chang, C. F., Gallia, G. L., Kerr, D. A., Johnson, E. M., Krachmarov, C. P., Barr, S. M., Frisque, R. J., Bollag, B. & Khalili, K. (1995c). Cooperative action of cellular proteins YB-1 and Pur a with the tumor antigen of the human JC polyomavirus determines their interaction with the viral lytic control element. Proc Natl Acad Sci U S A 92, 1087–1091. Dahl, R., Ramirez-Bergeron, D. L., Rao, S. & Simon, M. C. (2002). Spi-B can functionally replace PU.1 in myeloid but not lymphoid development. EMBO J 21, 2220–2230. Damania, B. & Alwine, J. C. (1996). TAF-like function of SV40 large T antigen. Genes Dev 10, 1369–1381. Daniel, A. M. & Frisque, R. J. (1993). Transcription initiation sites of prototype and variant JC virus early and late messenger RNAs. Virology 194, 97–109. Daniel, A. M., Swenson, J. J., Mayreddy, R. P., Khalili, K. & Frisque, R. J. (1996). Sequences within the early and late promoters of archetype JC virus restrict viral DNA replication and infectivity. Virology 216, 90–101. Dekoninck, A., Calomme, C., Nizet, S., de Launoit, Y., Burny, A., Ghysdael, J. & Van Lint, C. (2003). Identification and characterization of a PU.1/Spi-B binding site in the bovine leukemia virus long terminal repeat. Oncogene 22, 2882–2896. Dorn, A., Fehling, H., Koch, W., le Meur, M., Gerlinger, P., Benoist, C. & Mathis, D. (1988). B-cell control region at the 59 end of a major histocompatibility complex class II gene: sequences and factors. Mol Cell Biol 8, 3975–3987. Erselius, J. R., Jostes, B., Hatzopoulos, A. K., Mosthaf, L. & Gruss, P. (1990). Cell-type-specific control elements of the lymphotropic papovavirus enhancer. J Virol 64, 1657–1666. Frisque, R. J. (1983). Regulatory sequences and virus-cell interactions of JC virus. Prog Clin Biol Res 105, 41–59. Frisque, R. J., Bream, G. L. & Cannella, M. T. (1984). Human polyomavirus JC virus genome. J Virol 51, 458–469. Garrett-Sinha, L. A., Su, G. H., Rao, S., Kabak, S., Hao, Z., Clark, M. R. & Simon, M. C. (1999). PU.1 and Spi-B are required for normal B cell receptor-mediated signal transduction. Immunity 10, 399–408. Garrett-Sinha, L. A., Hou, P., Wang, D., Grabiner, B., Araujo, E., Rao, S., Yun, T. J., Clark, E. A., Simon, M. C. & Clark, M. R. (2005). Spi-1 and Spi-B control the expression of the Grap2 gene in B cells. Gene 353, 134–146. Gerster, T., Matthias, P., Thali, M., Jiricny, J. & Schaffner, W. (1987). Cell type-specificity elements of the immunoglobulin heavy chain gene enhancer. EMBO J 6, 1323–1330. Gosert, R., Kardas, P., Major, E. O. & Hirsch, H. H. (2010). Rearranged JC virus non-coding control regions found in progressive multifocal leukoencephalopathy increase virus early gene expression and replication rate. J Virol 84, 10448–10456. Gruda, M. C., Zabolotny, J. M., Xiao, J. H., Davidson, I. & Alwine, J. C. (1993). Transcriptional activation by simian virus 40 large T antigen: interactions with multiple components of the transcription complex. Mol Cell Biol 13, 961–969. Hagemeier, C., Bannister, A. J., Cook, A. & Kouzarides, T. (1993). The activation domain of transcription factor PU.1 binds the retinoblastoma (RB) protein and the transcription factor TFIID in vitro: RB shows sequence similarity to TFIID and TFIIB. Proc Natl Acad Sci U S A 90, 1580–1584. Journal of General Virology 91