Reconstitution of an Escherichia coli repair endonuclease activity from the separated uvrA+ and uvrB+/uvrC+ gene products.

An in vitro complementation assay has been used for partial purification of uvrA+, uvrB+, and uvrC+ gene products from Escherichia coli. The uvrB+ and uvrC+ products cochromatograph on DEAE-cellulose and are completely resolved from the uvrA+ product, which has been further purified by phosphocellulose chromatography of the nonadsorbed protein fraction from the DEAE-cellulose. Neither the uvrB+/uvrC+ nor the uvrA+ product shows appreciable endonuclease activity on UV-irradiated DNA when tested separately. However, these factors complement each other to yield and ATP-dependent endonuclease activity specific for UV-irradiated DNA. Gel filtration experiments with the partially purified proteins indicate that the functional uvrA+ gene product has a molecular weight of 100,000. The uvrB+ gene product has an apparent molecular weight of 70,000, but it is presently unclear if this is the size of the uvrB+ product alone or the size of a complex of the uvrB+ and uvrC+ gene products.