Coordinating DNA replication initiation with cell growth: differential roles for DnaA and SeqA proteins

Area of Science:

• Bacterial cell cycle regulation
• DNA replication initiation
• Microbial physiology

Background:

• The bacterial cell cycle, particularly DNA replication control in Escherichia coli, is crucial for cell division and proliferation.
• Understanding the precise timing and regulation of DNA replication initiation is key to bacterial growth dynamics.

Purpose of the Study:

• To develop and apply a novel analytical approach for studying Escherichia coli replication control.
• To investigate the role of the SeqA protein in regulating DNA replication initiation.
• To elucidate the interplay between cell growth, division, and DNA replication.

Main Methods:

• Culturing Escherichia coli cells at low growth rates to approximate eukaryotic cell cycle phases.
• Utilizing flow cytometry to analyze cell mass and determine the timing of replication initiation.
• Comparing wild-type, seqA mutant, and dnaA(Ts) mutant strains to assess regulatory mechanisms.

Main Results:

• Replication initiation in wild-type E. coli is tightly coupled to cell physiology, with a narrow distribution of cell masses at initiation (CV < 9%).
• The seqA mutant initiates DNA replication at a 10-20% lower cell mass compared to wild-type, confirming SeqA as a negative regulator.
• dnaA(Ts) mutants exhibit increased mass at initiation and higher variability, while seqA mutants can undergo multiple initiation events per cycle asynchronously.

Conclusions:

• SeqA acts as a negative regulator of DNA replication initiation in Escherichia coli.
• Cellular physiology, growth rate, and regulatory proteins like SeqA and DnaA significantly influence the timing and coordination of DNA replication.
• This study provides new insights into the complex regulatory network governing bacterial DNA replication and cell division.