THE TRAE GENE OF PLASMID RP4 ENCODES A HOMOLOG OF ESCHERICHIA-COLI DNA TOPOISOMERASE-III

The polypeptide encoded by the plasmid RP4 traE gene shows extensive p rotein sequence similarity to Escherichia coil topB, the gene encoding DNA topoisomerase III (Topo III), The traE gene product has been clon ed into a bacteriophage T7-based transient expression system, and the polypeptide has been expressed and purified, The TraE protein exhibits topoisomerase activity similar to that of Topo III, Relaxation is sti mulated by high temperature and low concentrations of Mg2+. In additio n, similar to E. coli Topo III, the TraE protein is a potent decatenas e and can substitute for Topo III activity in vivo. The biochemical pr operties of the TraE protein in vitro suggest that the protein may be involved in the resolution of plasmid DNA replication intermediates ei ther during vegetative replication or in conjugative DNA transfer, Put ative homologues of Topo III have been found to be encoded by other br oad host range, conjugative plasmids isolated from both Gram-negative and Gram-positive organisms, suggesting that Topo III-like polypeptide s may have an essential role in the propagation of many promiscuous pl asmids.