DNA modifying enzymes of Agrobacterium tumefaciens: effect of DNA topoisomerase, restriction endonuclease, and unique DNA endonuclease on plasmid and plant DNA.

Abstract
Extracts from A. tumefaciens strain IDI35 contain 3 enzymes that were characterized and partially purified. The 1st enzyme, a DNA topoisomerase, appeared to relax only negatively twisted DNA. The 2nd enzyme, Atu I, a type II restriction endonuclease, generated the identical DNA digestion pattern as EcoRII when several DNA were used. The 3rd enzyme, endonuclease A, showed a preference for superhelical DNA as substrates. When plasmid pCK135 DNA, obtained from the virulent strain 1D135 of A. tumefaciens, or plant DNA was exposed to the 3 enzymes, changes in DNA patterns were observed due to either conformational changes or digestion of the DNA. These enzymes may function in vivo in the processing and incorporation of bacterial DNA in plant cells.