Mike O'Donnell

SnapShot: The Replisome

Rho Factor: Transcription Termination in Four Steps

Rho factor is a hexameric ring-shaped helicase which terminates transcription in Escherichia coli. Two recent crystal structures of Rho in complex with nucleic acid reveal how this helicase ring loads onto mRNA and encircles it.

Toroidal proteins: Running rings around DNA

Recent structural data indicate that the toroidal form is quite common among DNA-binding enzymes. Is this abundance of ring-shaped proteins a coincidence, or does it reflect convergence to a winning quaternary structure?

DNA Ligase: Getting a Grip to Seal the Deal

The crystal structure of human DNA ligase I catches the enzyme just before the last step of ligation and shows that the protein wraps completely around nicked DNA. The elegant structure explains how ligase attains fidelity for the sealing operation.

Replicative helicase loaders: ring breakers and ring makers

Helicase loaders transfer the ring-shaped replicative helicases onto DNA. They assort into two classes: ring breakers, which place stabile hexameric rings on DNA via transient gaps at subunit interfaces; and helicase makers, which assemble hexameric rings around DNA from monomeric helicase units.