Figure 3.

LMB blocks the cell cycle in early G₁. (A) Phase contrast of unsynchronized HeLa cells treated for 2 hours with LMB. The number of early G₁ cells (doublet linked by a cytoplasm bridge) is high. (B) Percentage of early G₁ (black) depending on the duration of the LMB treatment compared to interphase (grey). The percentage increases with duration of treatment and can be maintained for up to 6 hours. (C) Cells blocked in early G₁ after 120 minutes of LMB. In nuclei several large dark structures (phase contrast) containing B23 (GFP-B23 labeling) correspond to incipient nucleoli. In addition B23 is observed in many PNBs. The cytoplasmic bridge with the mid-body is visible in upper image. (D) Traffic of B23/NPM measured by photoactivation in early G1a for 2 minutes. Relative intensity in the activated incipient nucleoli, in control black curve and in LMB-treated cells (2 h) red curve (mean of 8 CTR and 10 LMB-treated cells). (E) Comparison of the t_1/2 of B23/NPM traffic in incipient nucleoli of early G₁ and interphase nucleoli in control (CTR) and LMB-treated (LMB) cells.