A SMALLER FORM OF THE SLIDING CLAMP SUBUNIT OF DNA-POLYMERASE-III IS INDUCED BY UV IRRADIATION IN ESCHERICHIA-COLI

The beta subunit of DNA polymerase III holoenzyme of Escherichia coli is a 40.6-kDa protein that functions as a sliding DNA clamp (Stukenber g, P. T., Studwell-Vaughan, P. S., and O'Donnell, M. (1991) J. Biol. C hem. 266, 11328-11334), It is responsible for tethering the polymerase to DNA and endowing it with the high processivity required For DNA re plication, 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 beta subunit, contains an internal in-frame gene, termed dnaN, that encodes a smaller form of the beta subunit. The novel 26-kDa protein, termed beta, is UV-induci ble, 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 beta protein functions in a reaction associ ated with DNA repair or recovery of DNA replication in UV-irradiated c ells.