Monoclonal antibodies specific for the tau subunit of the DNA polymerase III holoenzyme of Escherichia coli. Use to demonstrate that tau is the product of the dnaZX gene and that both it and gamma, the dnaZ gene product, are integral components of the same enzyme assembly.

We have established two murine hybridoma cell lines that secrete monoclonal antibodies directed against the tau subunit of the DNA polymerase III holoenzyme of Escherichia coli. Both antibodies have been purified and identified to be of the IgG1 class. Competition assays indicate that they bind to two distinct portions of the tau subunit. These antibodies have been used to demonstrate that tau is an integral part of all DNA polymerase III holoenzyme assemblies and that tau is the product of the dnaZX gene. Both of the antibodies react only with tau, not with gamma, the other protein product of the dnaZX gene. Immunoprecipitation studies demonstrated that tau is contained within the same enzyme assemblies as gamma (dnaZ protein). This observation is discussed in the light of the DNA polymerase III holoenzyme functioning as an asymmetric dimer, capable of coordinating leading with lagging strand replication.