The Effect of Lysogenic Induction on the Deoxyribonucleases of Escherichia Coli K12-lambda. I. Appearance of a New Exonuclease Activity.

Infection of Escherichia coli cells with bacteriophages of the T series has been shown to result in a large rise in deoxyribonuclease activity (1, 2). Wormser and Pardee have reported that although T2 infection of E. coli K12X causes a 4to 8-fold increase in deoxyribonuclease (DNase) activity of the cells, lysogenic induction of these cells by ultraviolet light causes no significant increase in DNase activity (3). We have found that lysogenic induction of E. coli K12X by mitomycin C or by thymine deprivation (4) causes an approximately lo-fold rise in DNase specific activity observable at pH 10 in crude extracts. This elevated DNase activity is not seen when nonlysogenic cells of K12 (K12S) are treated with mitomycin C. Infection of K12S cells with a lethal mutant of X (X C-57), however, does cause a large increase in DNase activity at pH 10 in crude extracts of the infected cells. This increased DNase activity therefore seems to be specifically associated with lysogenic induction and the formation of the phage X. The DNase responsible for this rise in activity has been isolated, and evidence will be presented that this is a new exonuclease activity which is not detected in extracts of normal, uninduced E. coli K12X. Three other DNases have also been separated from lysogenically induced cells of E. coli K12X and have been found to be similar to the corresponding nucleases isolated from uninduced cells (5). A preliminary communication of this work has appeared (6).