The Rtf1/Prf1-dependent histone modification axis counteracts multi-drug resistance in fission yeast

Area of Science:

• Molecular Biology
• Gene Regulation
• Eukaryotic Transcription

Background:

• RNA polymerase II transcription elongation involves histone modifications like H2B monoubiquitylation and H3K4 methylation.
• The Rtf1 elongation factor initiates a regulatory cascade impacting these histone modifications.
• The precise role of this axis in gene expression and cellular phenotypes remained unclear.

Purpose of the Study:

• To investigate the functional significance of the Rtf1-H2Bub1-H3K4me axis in gene regulation.
• To explore the connection between this axis and drug resistance phenotypes in *Schizosaccharomyces pombe*.
• To determine if mutations in the RNA polymerase II C-terminal repeat domain share regulatory functions.

Main Methods:

• Utilized *Schizosaccharomyces pombe* as a model eukaryote.
• Introduced mutations affecting the Rtf1-H2Bub1-H3K4me axis and RNA polymerase II C-terminal repeat domain.
• Assessed phenotypes including hydroxyurea (HU) resistance, dNTP pool dynamics, S-phase checkpoint response, and transcriptional responses to HU.
• Tested azole antifungal agent sensitivity.

Main Results:

• Mutations in the Rtf1-H2Bub1-H3K4me axis conferred resistance to hydroxyurea (HU).
• HU resistance correlated with altered dNTP pools, reduced S-phase checkpoint reliance, and blunted transcriptional responses to HU.
• Mutations in the Rpb1 C-terminal repeat domain mimicked these HU resistance phenotypes.
• All investigated mutants displayed cross-resistance to azole antifungal agents.

Conclusions:

• The Rtf1-H2Bub1-H3K4me axis and the Rpb1 C-terminal repeat domain share a gene regulatory function.
• This shared function is critical for controlling fungal drug tolerance.
• These findings reveal a novel link between transcription elongation machinery and antifungal drug resistance.