NUCLEAR-DNA TOPOISOMERASES IN PISUM-SATIVUM L

This paper demonstrates that in nuclei of root meristems of Pisum sativum L. there are at least two, and possibly three, different DNA topoisomerases. One enzyme is unbound by the Mono Q ion exchange column and seems to be similar to eukaryotic type I DNA topoisomerases. The other 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 column. 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 filtration peak together with other proteins, including endodeoxyribonuclease, indicating that they might form a native multiprotein complex. The nature, occurrence in vivo, and the functional role of this complex remain to be investigated. Nevertheless, the presence of different DNA topoisomerases in the same meristematic tissue might suggest that different types of topological transformation are required for different activities of DNA, such as replication, transcription and chromosome segregation.