Some evidence for replication-transcription coupling in Physarum polycephalum

Area of Science:

• Molecular Biology
• Cell Cycle Regulation
• Biochemistry

Background:

• Hydroxyurea is a known inhibitor of DNA synthesis.
• The precise mechanisms and cell cycle specificity of hydroxyurea's effects on DNA and RNA synthesis require further elucidation.

Purpose of the Study:

• To investigate the selective effects of hydroxyurea on DNA and RNA synthesis during different phases of the cell cycle.
• To explore the relationship between DNA replication and RNA transcription.

Main Methods:

• Treatment of cells with hydroxyurea (40-60 mM) during various cell cycle phases.
• Measurement of thymidine incorporation into DNA.
• Measurement of uridine incorporation into total RNA and specific RNA fractions (rRNA, poly(A)-rich RNA).
• Analysis using DNA-RNA hybridization.

Main Results:

• Hydroxyurea selectively inhibited thymidine incorporation into DNA within 5-10 minutes during ongoing S-phase.
• DNA replication initiation at the start of S-phase and DNA synthesis in G2 phase were unaffected.
• Uridine incorporation into RNA was significantly inhibited (up to 70%) in early S-phase.
• This RNA synthesis inhibition was confirmed for rRNA and poly(A)-rich RNA fractions.
• RNA synthesis inhibition persisted even when DNA maturation was blocked by cycloheximide.

Conclusions:

• Hydroxyurea acts as a selective inhibitor of DNA synthesis during S-phase.
• Early S-phase RNA synthesis is particularly sensitive to hydroxyurea.
• Replicating chromatin early in S-phase may serve as a more efficient template for transcription.