NUCLEAR-DNA TOPOISOMERASES IN PISUM-SATIVUM L

This paper demonstrates that in nuclei of root meristems of Pisum sati vum L. there are at least two, and possibly three, different DNA topoi somerases. One enzyme is unbound by the Mono Q ion exchange column and seems to be similar to eukaryotic type I DNA topoisomerases. The othe r two enzymes are both retained by the Mono Q ion exchange column but they may be separated by their affinities for a single-strand DNA colu mn. Both enzymes are difficult to classify, but it is likely that one of them is a type II topoisomerase. Prior to fractionation on Mono Q, all these different DNA topoisomerases clute in the same gel filtratio n peak together with other proteins, including endodeoxyribonuclease, indicating that they might form a native multiprotein complex. The nat ure, occurrence in vivo, and the functional role of this complex remai n to be investigated. Nevertheless, the presence of different DNA topo isomerases in the same meristematic tissue might suggest that differen t types of topological transformation are required for different activ ities of DNA, such as replication, transcription and chromosome segreg ation.