MULTIPLE BACTERIAL TOPOISOMERASES - SPECIALIZATION OR REDUNDANCY

In the past few years, two new DNA topoisomerases have been discovered in bacteria, bringing the total number of DNA topoisomerases in E. co li to four. Two classes of topoisomerases, type 1 and type 2, are dist inguishable by their amino acid homology and their apparent reaction m echanism. Of the four E. coli topoisomerases, there are two type 1 and two type 2 enzymes. In eukaryotes, the existence of multiple type 1 a nd type 2 enzymes has also become apparent. The existence of these mul tiple enzymes provokes a question whose answer has both evolutionary a nd physiological implications: are these topoisomerases functionally r edundant, or have they acquired sufficient specialization that they no w perform unique biological reactions? In bacteria, there is evidence for both specialization and redundancy in the functions of topoisomera ses.