Transcription coordinates histone amounts and genome content

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Cell survival depends on stable protein concentrations, typically achieved by linking synthesis rates to cell volume.
• Genomic DNA content doubles during the cell cycle and increases with ploidy, independent of cell volume.
• Most proteins scale with cell volume, but DNA content does not, creating a potential imbalance.

Purpose of the Study:

• To investigate how histone protein levels are coordinated with DNA content, despite global synthesis scaling with cell volume.
• To understand the regulatory mechanisms underlying histone homeostasis in relation to cell volume and ploidy.
• To determine if this coordination is intrinsic to histone gene regulation.

Main Methods:

• Analysis of histone mRNA and protein synthesis rates in relation to cell volume and ploidy.
• Mathematical modeling of gene regulation mechanisms.
• Experimental manipulation using histone promoter truncations.

Main Results:

• Histone protein amounts are coupled to DNA content, not cell volume.
• Histone concentrations decrease with increasing cell volume but increase with ploidy.
• This regulation is established at the transcript level via histone promoters, without requiring feedback loops.
• A balance between transcription initiation and elongation rates controls gene dependence on cell volume and ploidy.

Conclusions:

• Histone homeostasis is uniquely coordinated with genome content, diverging from global protein scaling rules.
• The regulation of histone levels is an intrinsic property of histone promoters, ensuring accurate genome maintenance.
• A fundamental mechanism involving transcription initiation and elongation balances controls gene expression relative to cell volume and ploidy.