Spontaneous formation of nucleus-like structures around bacteriophage DNA microinjected into Xenopus eggs.

We have found that injection of bacteriophage lambda DNA into unfertilized Xenopus eggs causes the assembly around the DNA of structures resembling typical eucaryotic cell nuclei. These spherical structures begin to form 60-90 min after injection. They contain lambda DNA and are bounded by a phase-dense envelope. Immunofluorescent staining of the lambda-DNA-containing structures with anti-lamin antibody reveals the presence of the lamin nuclear proteins at the periphery of the structure, a pattern identical to that of embryonic nuclei. Electron microscopy reveals that the injected DNA is surrounded by a double bilayer nuclear membrane containing nuclear pore complexes. The "nuclei" containing lambda DNA respond to modulators of the Xenopus cell cycle in a manner that mimics the response of embryonic nuclei to these modulators during mitosis. These results suggest that nuclear reassembly and breakdown occur independently of specific DNA sequence information.