A smaller form of the sliding clamp subunit of DNA polymerase III is induced by UV irradiation in Escherichia coli

Abstract

The β subunit of DNA polymerase III holoenzyme of Escherichia coli is a 40.6-kDa protein that functions as a sliding DNA clamp (Stukenberg, P. T., Studwell-Vaughan, P.S., and O'Donnell, M. (1991) J. Biol. Chem. 266, 11328- 11334). It is responsible for tethering the polymerase to DNA and endowing it with the high processivity required for DNA replication. Here and in a companion study (Paz-Elizur, T., Skaliter, R., Blumenstein, S., and Livneh, Z. (1996) J. Biol. Chem. 271, 2482-2490) we report that the dnaN gene, encoding the β subunit, contains an internal in-frame gene, termed dnaN*, that encodes a smaller form of the β subunit. The novel 26-kDa protein, termed β*, is UV-inducible, and when overexpressed from a plasmid under an inducible promoter, it increases up to 6-fold the UV resistance of E. coli cells. These findings suggest that the β* protein functions in a reaction associated with DNA repair or recovery of DNA replication in UV-irradiated cells.