Nucleocytoplasmic exchanges during early interphase.

Colloidal gold was injected into the cytoplasm of amebae (Amoeba proteus) approximately 5 min, 1 hr, and 2 hr after cytokinesis. Later, interphase cells were similarly treated. All of the amebae were fixed about 50 min after injection and were examined with the electron microscope in order to determine the distribution of the gold. It was found that for a period of 2 hr after division the uptake of gold by the nuclei was significantly greater than that during late interphase. Correlation of the gold distribution with the morphology of the nuclear envelope indicated that an inverse relationship exists between the rate of incorporation of colloid into the nucleoplasm and the degree of reconstitution of the fibrous lamina ("honeycomb" structure). These data support the view that the fibrous lamina functions in regulating nucleocytoplasmic exchanges.