Nucleoid-associated proteins affect mutation dynamics in E. coli in a growth phase-specific manner

Area of Science:

• Genomics
• Microbial genetics
• Evolutionary biology

Background:

• DNA-binding proteins can protect DNA from damage but may hinder repair processes.
• The impact of DNA-binding proteins on intra-genomic mutation rate differences and sequence variation is not well understood.
• Nucleoid-associated proteins (NAPs) play crucial roles in bacterial genome organization and regulation.

Purpose of the Study:

• To investigate how the binding of four abundant nucleoid-associated proteins (Fis, H-NS, IhfA, and IhfB) affects DNA mutability and sequence evolution in Escherichia coli.
• To determine if protein occupancy correlates with increased or decreased mutation rates.
• To understand the role of NAPs in shaping extant sequence variation within E. coli populations.

Main Methods:

• Analysis of sequence evolution in E. coli.
• Examination of DNA mutability in relation to the binding patterns of Fis, H-NS, IhfA, and IhfB.
• Correlation of protein occupancy with mutation rates across different stages of the bacterial growth cycle.

Main Results:

• Protein occupancy was associated with both increased and decreased mutability for a subset of mutations, dependent on the timing of protein binding during the bacterial growth cycle.
• On average, DNA bound by these proteins showed reduced mutability compared to unbound DNA.
• The protective effect of protein binding was weak and could be negated or reversed when binding coincided with DNA repair activity.

Conclusions:

• The four analyzed nucleoid-associated proteins have a minor but significant role in shaping current sequence variation in E. coli.
• The interplay between protein binding and DNA repair dynamics influences the net effect on mutability.
• Understanding these dynamics is crucial for comprehending genome evolution in bacteria.