The DinG protein from Escherichia coli is a structure-specific helicase

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The DinG protein from Escherichia coli is a DNA damage-inducible helicase belonging to superfamily 2.
• Helicases are crucial enzymes that unwind nucleic acid duplexes, playing vital roles in DNA replication, repair, and recombination.

Purpose of the Study:

• To systematically investigate the structural requirements for DNA unwinding by the Escherichia coli DinG protein.
• To determine potential in vivo roles for DinG based on its substrate specificity.

Main Methods:

• Utilized a panel of synthetic DNA substrates with varying structures (blunt ends, ss tails, flaps, D-loops, R-loops).
• Assessed the helicase activity of purified DinG on these synthetic substrates.
• Investigated DinG's activity on D-loops formed by RecA.

Main Results:

• DinG requires a 5' single-stranded DNA tail of 11-15 nucleotides to initiate unwinding; blunt ends and 3' ss tails are not substrates.
• DinG unwinds 5'-flap structures but not 3'-flap structures.
• DinG efficiently unwinds DNA:RNA duplexes, D-loops, and R-loops, with activity on RecA-formed D-loops suggesting a natural substrate role.

Conclusions:

• DinG's strict requirement for 5' ssDNA tails for duplex unwinding, alongside its activity on D-loops and forked structures, suggests involvement in homologous recombination and replication restart after DNA damage.
• DinG may function in recombinational DNA repair pathways and in resuming replication forks stalled by DNA damage.