SERRATE drives phase separation behaviours to regulate m6A modification and miRNA biogenesis.

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• The methyltransferase complex (MTC) mediates N6-adenosine (m⁶A) RNA modification.
• The microprocessor complex is essential for microRNA biogenesis.
• Cross-regulation between MTC and microprocessor remains largely unexplored.

Purpose of the Study:

• To investigate the interplay between MTC and the microprocessor.
• To elucidate the role of phase separation in coordinating RNA modification and processing.

Main Methods:

• Analysis of MTC subunit B solubility and activity.
• Characterization of SERRATE (SE) condensate properties.
• Assessment of m⁶A levels in SE variants.
• Investigation of microprocessor recruitment to miRNA loci.
• Examination of m⁶A reader enrichment on pri-miRNA substrates.

Main Results:

• MTC subunit B forms insoluble condensates, regulated by the proteasome.
• SE forms liquid-like condensates that enhance MTC subunit B solubility, stability, and activity.
• SE variants impairing MTC interaction or phase behavior reduce m⁶A levels.
• MTC recruits the microprocessor to miRNA loci for co-transcriptional cleavage.
• m⁶A modifications on pri-miRNAs recruit m⁶A readers, retaining the microprocessor for processing.

Conclusions:

• Phase separation driven by SE is crucial for MTC activity and m⁶A modification.
• MTC and microprocessor exhibit reciprocal regulation, coordinating RNA processing.
• This study reveals a novel mechanism of phase separation in RNA modification and processing.