Use of an Escherichia coli mutant strain permits measurement of single-stranded apurinic-apyrimidinic endonuclease in crude extracts: studies with untransformed cells and cells transformed with plasmids containing the uvrC gene.

We have constructed a strain of Escherichia coli that is defective in exonuclease VII and uracil-DNA glycosylase activities. This strain (xse ung) facilitates the quantitation of single-stranded apurinic-apyrimidinic endonuclease activity in crude extracts. Quantitative comparisons of single-stranded apurinic-apyrimidinic endonuclease activity under conditions in which uvrC protein is overexpressed showed no differences, suggesting that single-stranded apurinic-apyrimidinic endonuclease and uvrC protein are probably distinct.