Purification of an endonuclease from adenovirus-infected KB cells

This report describes the purification of an endonuclease from extracts of adenovirus-type-2-infected KB cells. Endonuclease activity can also be detected in extracts of uninfected KB cells and the enzyme activities from extracts of uninfected and adenovirus-infected cells are very similar, if not identical. The enzyme has its maximal activity at pH 4.0. The enzyme found in uninfected and adenovirus-infectedcells is, however, strikingly different from an endonuclease isolated from calf serum. Hence, the endonuclease described is probably not a contaminant derived from the medium in which the KB cells were propagated. The endonuclease in crude extracts from uninfected or adenovirus-infected KB cells can be activated or its activity enhanced by treatment of the extracts with proteolytic enzymes, like pronase or trypsin. Evidence has been presented suggesting that this activation is due to proteolytic cleavage of an inhibitor present in crude extracts of uninfected and adenovirus-type-2-infected KB cells. A second endonuclease has been found in extracts of infected and uninfected cells with optimal activity at pH 7.2 and this endonuclease can be separated from the one with a pH optimum at 4.0.