No abstract

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-infected cells 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.In previous work an endonuclease specific for double-stranded DNA has been described in association with the penton subunit of adenovirus type 2 [l], in extracts of KB cells infected with adenovirus types 2 and 12 and in association with purified

The properties of the pH 4.0 endonuclease from adenovirus‐type‐2‐infected KB cells were determined. The enzyme has a molecular weight of approximately 40 000. Its pH optimum is at pH 4.0, it is not inhibited by ethylenediaminetetraacetate (EDTA), and it is active at temperatures up to 60 °C. The enzyme cleaves adenovirus DNA in a stepwise manner. The limit digestion product has a molecular weight of 120 000–200 000. There is evidence that the cleavage reaction proceeds via an initial single‐strand nick. Under the conditions tested the endonuclease did not seem to reveal a high degree of specificity as to the recognition of cleavage sites, or else the sites recognized occurred very frequently.