both endogenous and exogenous Flag tagged YY1. The upper band indicates Flag-tagged exogenous YY1 and the lower band indicates endogenous YY1. (TIF) Figure S2 VDJ rearrangements are similar in MigR1 vector and MigR1-FlagYY1 transduced B cells from reconstituted animals. Rearrangement of various VH gene families is shown comparing mice reconstituted with MigR1 vector alone or MigR1-FlagYY1. V gene and DJ rearrangements are not altered by YY1 expression. (TIF) Figure S3 Confirmation of YY1 overexpression micro- array results by RT-PCR. Microarray results (black bars) shown as fold change increase or decrease of MigR1-FlagYY1 transduced 38B9 cells relative to MigR1 vector alone, are compared with fold changes measured by RT-PCR (stippled bars). Error bars show the standard deviation of the mean. All transcripts matched closely by the two methods except for nanog expression which was induced to a much lower level as determined by RT-PCR. 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Genes Dev 21: 1179–1189. 32. Calame K, Atchison M (2007) YY1 helps bring loose ends together. Genes Dev 21: 1145–1152. PLoS ONE | www.plosone.org 12 January 2012 | Volume 7 | Issue 1 | e30656