DNA synthesis by the isolated nuclear matrix from synchronized plasmodia of Physarum polycephalum

Cell cycle-dependent activation of telomerase in naturally synchronized culture of a true slime mold, Physarum polycephalum

Telomeres of Physarum plasmodia did not shorten with numerous repeats of nuclear division, and an apparent activity of telomerase was detected in this organism. In naturally synchronized culture of Physarum plasmodia, an evident activation of telomerase was observed at the late S-phase, just prior to the completion of in vivo DNA replication, and the low telomerase activity was detected throughout the cell cycle. In the nuclei isolated from different phases of synchronized plasmodia, a higher activity of telomerase was also observed at late S-phase. These results clearly show the existence of a cell cycle-dependent regulatory mechanism of telomerase activity in growing, naturally synchronized cells.

Nuclear matrix and the cell cycle

The facts that the nuclear matrix represents a structural framework of the cell nucleus and that nuclear events, such as DNA replication, transcription, and DNA repair, are associated with this skeletal structure suggest that its components are subject to cell cycle-regulatory mechanisms. Cell cycle regulation has been shown for nuclear lamina assembly and disassembly during mitosis and chromatin reorganization. Little attention has so far been paid to internal nuclear matrix proteins and matrix-associated proteins with respect to the cell cycle. This survey attempts to summarize available data and presents experimental evidence that important metabolic functions of the nucleus are regulated by the transient, cell cycle-dependent attachment of enzymes and regulatory proteins to the nuclear matrix. Results on thymidine kinase and RNA polymerase during the synchronous cell cycle of Physarum polycephalum demonstrate that reversible binding to the nuclear matrix represents an additional level of regulation for nuclear processes.