Fig. 4.

Acquisition of nuclear actin relative to nuclear pores, lamina formation, and DNA synthesis during nuclear assembly in vitro. Nuclei from Xenopus egg extract reactions spiked with fluorescent actin (red) were isolated at the times indicated, fixed, and probed with mAb414 against nuclear pore proteins (A, green) or antibody L₀46F7 against lamin (B, green). DNA synthesis was detected with anti-BrdUrd (C, green). Controls without BrdUrd had no detectable green signals. In merged images of mature nuclei, BrdUrd signals coincide with DNA (blue) as expected (aqua), and actin appears noncoincident. Diffuse actin and irregularly distributed pores are detected at 30 min, lamin epitopes at 40 min, and BrdUrd at 50 min. Assembly times vary with extract, but the relative sequence of actin acquisition, pore assembly, lamina formation, and DNA synthesis was maintained in three independent experiments.