tau binds and organizes Escherichia coli replication proteins through distinct domains - Partial proteolysis of terminally tagged tau to determine candidate domains and to assign domain V as the alpha binding domain

The tau subunit dimerizes Escherichia coli DNA polymerase III core through interactions with the a:subunit. In addition to playing critical roles in t he structural organization of the holoenzyme, tau mediates intersubunit com munications required for efficient replication fork function. We identified potential structural domains of this multifunctional subunit by limited pr oteolysis of C-terminal biotin-tagged I proteins, The cleavage sites of eac h of eight different proteases were found to be clustered within four regio ns of the tau subunit, The second susceptible region corresponds to the hin ge between domain II and III of the highly homologous S' subunit, and the t hird region is near the C-terminal end of the tau-delta' alignment (Guenthe r, B., Onrust, R., Sali, A., O'Donnell, M., and Kuriyan, J. (1997) Cell 91, 335-345), We propose a five-domain structure for the tau protein, Domains I and II are based on the crystallographic structure of delta' by Guenther and colleagues. Domains III-V are based on our protease cleavage results, U sing this information, we expressed biotin-tagged tau proteins lacking spec ific protease-resistant domains and analyzed their binding to the a subunit by surface plasmon resonance, Results from these studies indicated that th e alpha binding site of tau lies within its C-terminal 147 residues (domain V).