DNA repair in Escherichia coli: identification of the uvrD gene product.

A 2.9-kilobase (kb) Pvu II DNA fragment that contains the uvrD gene of Escherichia coli K-12 has been cloned in both low-copy and multiple-copy plasmid vehicles. The low-copy uvrD plasmid (pVMK49) complements a variety of uvrD, uvrE, and recL mutations. In contrast, the same strains carrying the 2.9-kb fragment in a multiple-copy plasmid (pVMK45) remain sensitive to ultraviolet light (UV). Additionally, pVMK45 transformants of wild-type E. coli are sensitive to UV and methyl methanesulfonate and appear to be recombination deficient. The cloned uvrD gene does not complement the dominant uvrD3 allele. The 2.9-kb Pvu II insert in these plasmids encodes a single 76,000-dalton protein, which, on the basis of insertional inactivation experiments with the Tn1000 transposon, must be the uvrD gene product. These data confirm earlier genetic analysis which suggested that recL, uvrE, and uvrD were all allelic. The direction of transcription of the uvrD gene has also been determined.