Threonine 39 phosphorylation on YY1 peaks at G2/M transition.

<p>Stable HeLa-Flag-YY1 cells were synchronized by double-thymidine block and then released. (<b>A</b>) Analysis of the cell-cycle progression of HeLa cells released after double-thymidine block using fluorescence-activated cell sorting. Cells were stained with propidium iodide and analyzed based on their DNA content. An asynchronous population of cells was used as a control. (<b>B</b>) Whole cell extracts were prepared from HeLa-Flag-YY1 cells collected at the indicated times after release from double-thymidine block. Total WCE were analyzed on a Western blot after SDS-PAGE separation, and probed with anti-Plk1, anti-Cyclin B1, and anti-YY1 antibodies. Flag-YY1 was immunoprecipitated from the extracts of each time point, and then analyzed on a Western blot using anti-pT39 and anti-YY1 antibodies.