More evidence for replication-transcription-coupling in Physarum polycephalum

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• RNA polymerases are crucial enzymes for gene transcription.
• Understanding their activity during the cell cycle provides insights into gene regulation.
• Physarum polycephalum is a model organism for studying nuclear processes.

Purpose of the Study:

• To investigate endogenous RNA polymerase activity in Physarum polycephalum nuclei.
• To compare RNA polymerase A and B activities across different mitotic cycle stages.
• To determine the effect of DNA synthesis inhibition on RNA polymerase activity.

Main Methods:

• Isolated nuclei from Physarum polycephalum macroplasmodia were used.
• RNA polymerase activity was assayed at high (400 mM KCl) and low (5-100 mM KCl) ionic strengths.
• Alpha-amanitin sensitivity was used to differentiate RNA polymerase B from RNA polymerase A (plus C).
• Hydroxyurea was used in vivo to inhibit DNA synthesis.

Main Results:

• Total RNA polymerase activity was minimal in metaphase nuclei.
• RNA polymerase B activity remained constant at high ionic strength across most stages.
• At low ionic strength, RNA polymerase B activity peaked in S-phase and early prophase, and was low in G2-phase.
• Hydroxyurea treatment drastically inhibited RNA polymerase activity in S-phase nuclei.

Conclusions:

• RNA polymerase activity in Physarum polycephalum is cell cycle-dependent.
• Ionic strength influences the observed RNA polymerase activity profiles.
• DNA synthesis is tightly linked to RNA polymerase activity, particularly during S-phase.