Blockage of the fork is dependent on the expression of the Ter binding protein, Tus, encoded on another plasmid, in which the tus gene is under the control of the ara promoter.
The Tus protein of Escherichia coli is capable of arresting DNA replication in an orientation-dependent manner when bound to specific sequences in the bacterial chromosome called Ter sites.
In addition to the site-directed mutagenesis studies, the tus genes of Salmonella, Klebsiella, and Yersinia were sequenced and the proteins expressed in E.