Expression of the Drosophila type II topoisomerase is developmentally regulated

The expression of the type II topoisomerase from Drosophila melanogaster was studied during development and in tissue culture cells. RNA blot and protein blot analyses using probes specific for Drosophila topoisomerase II show that the enzyme is developmentally regulated. Levels of both RNA transcript and protein appear highest during early embryogenesis and pupation, periods which are known to have the highest mitotic activity. Tissue culture analysis using Drosophila Kc cells supports these results as levels of topoisomerase II message are higher in rapidly dividing cells than in quiescent cells. Analysis of topoisomerase II levels in early embryos suggests that levels are adequately high for the enzyme to act in DNA replication or segregation at termination of replication. Apparent in vivo proteolysis of topoisomerase II is seen throughout the life cycle, in spite of careful precautions. Whether these proteolytic fragments are important in vivo is still uncertain.