Terminal cross-linking of DNA strands by an enzyme system from Escherichia coli infected with bacteriophage T4.

An enzyme system, purified 560-fold from Escherichia coli infected with bacteriophage T4, catalyzes the formation of a phosphodiester bond between the original 5'-phosphoryl end-group of a DNA strand and a 3'-hydroxyl group of the complementary strand. The product, a terminally cross-linked, spontaneously renaturable DNA duplex, has been characterized by chromatographic analysis, by sedimentation analysis, and by enzymatic digestion. Essential components of the enzyme system, which requires both ATP and Mg(++), include the T4-induced DNA ligase and a component found in extracts of uninfected E. coli, which is probably an exonuclease.