Human CRL2^ZYG11A/B is required for mitotic progression in cells overexpressing cyclin B1. (A) DIC micrographs of U2OS cells treated with the indicated siRNAs as they progress through mitosis. Timing in minutes is shown in the top right corner of images; the 0 time point denotes nuclear envelope breakdown. The last time point reflects mitotic exit. Bars, 20 µm. (B) Bar graph of mitotic timing ± SEM for siRNA-treated U2OS cells. Timing data from two to four independent experiments are summarized in the graph; for the conditions listed from top to bottom, n = 19, 18, 22, and 29, respectively. (C) Matching DIC and epifluorescence micrographs of U2OS cells expressing Venus–cyclin B1 treated with control and ZYG11A/B siRNA. (D) Bar graph of mitotic timing ± SEM for siRNA-treated U2OS cells expressing Venus–cyclin B1. Timing from three independent experiments are summarized in the graph; for conditions listed from top to bottom, n = 6 and 8, respectively. Bars, 20 µm. (E) Line graph of the level of Venus–cyclin B1 in cells as they progress through mitosis (times are after nuclear envelope breakdown); n = 6 and 8, as described in D. **, P < 0.01; ***, P < 0.001.