Nucleic acid metabolism in a slime mold with synchronous mitosis

Abstract

In the synchronously dividing slime mold, Physarum polycephalum, the synthesis of DNA as shown by incorporation of 14C fron [6- 14C]orotic acid into DNA-thymine, occured immediately after the nuclear division and lasted for 1–2 h. During the remainder of the interphase, which might last from 12–20 h, there was no significant labeling of the DNA. The incorporation of label into RNA at any time of the cell cycle suggested that RNA synthesis was continuous, although there was some indication that this process might be retarded at the time of division and DNA synthesis. The relative timing of DNA sythesis and nuclear division would tend to rule out the synthesis of DNA as a “trigger” for mitosis. Preliminary experiments indicated that the mold was capable of converting orotic acid to thymine nucleotides throughout the interphase; this suggests that the control of DNA synthesis must occur at some point very close to the final polymerization of the molecule.