a UV-inducible Smaller Form of the Subunit Sliding Clamp of DNA Polymerase III of Escherichia coli

• Published in: The Journal of biological chemistry 1996-02, Vol.271 (5), p.2482
• Main Authors: Tamar Paz-Elizur, Rami Skaliter, Sara Blumenstein, Zvi Livneh
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.5.2482

The 40.6-kDa β subunit of DNA polymerase III of Escherichia coli is a sliding DNA clamp responsible for tethering the polymerase to DNA and endowing it with high processivity (Stukenberg, P. T., Studwell-Vaughan, P. S., and O'Donnell, M.(1991) J. Biol. Chem. 266, 11328-11334). UV irradiation of E. coli induces a smaller 26-kDa form of the β subunit, termed β*, that, when overproduced from a plasmid, increases UV resistance of E. coli (Skaliter, R., Paz-Elizur, T., and Livneh, Z.(1996) J. Biol. Chem. 271, 2478-2481). Here we show that this protein is synthesized from a UV-inducible internal gene, termed dnaN *, that is located in-frame inside the coding region of dnaN , encoding the β subunit. The initiation codon and the Shine-Dalgarno sequence of dnaN * were identified by site-directed mutagenesis. The dnaN * transcript was shown to be induced upon treatment with nalidixic acid, and transcriptional dnaN*-cat gene fusions were UV inducible, suggesting induction of dnaN * at the transcriptional level. Analysis of translational dnaN*-lacZ gene fusions revealed that UV induction was abolished in strains carrying the recA56 , lexA3 , or Δ rpoH mutations, indicating involvement of both SOS and heat shock stress responses in the induction process. Expression of dnaN * represents a strategy of producing several proteins with related functional domains from a single gene.