Change of the nuclear pore frequency during the nuclear cycle of Physarum polycephalum.

The change of the nuclear pore frequency during the nuclear cycle of synchronous plasmodia of Physaru- polycephalum was investigated. Counts were made on platinum-carbon replicas of isolated nuclei. Pore numbers varied markedly at any given time of the nuclear cycle, possibly due to the variable DNA contents of the nuclei. The average pore frequency per nucleus increased from 336 at 1 h after mitosis to 770 at 50 min before the subsequent mitosis. The results suggest a quantitative relation between the nuclear DNA content and pore frequency. This is compatible with the hypothesis that pore complexes serve as attachment sites for nuclear DNA.