Since DNA topoisomerase II (EC 5.99.1.3) is an essential enzyme in yeast, 
heterologous topoisomerase II gene expression in yeast cells can provide a 
system for analyzing the structure and function of topoisomerase II genes from 
other species. A series of yeast expression plasmids was constructed in which 
segments of the cDNA sequences encoding Drosophila DNA topoisomerase II were 
inserted under the transcriptional control of yeast GAL1 promoter. Expression of 
the functional form of Drosophila topoisomerase II cDNA can complement 
conditionally lethal, temperature-sensitive mutations in the yeast topoisomerase 
II gene (TOP2), as well as mutations in which the TOP2 locus was disrupted. The 
survival of these yeast cells depends upon the continuous expression of 
Drosophila topoisomerase II. Repression of Drosophila gene expression by glucose 
causes these yeast cells to cease dividing after a few generations. In addition 
to these genetic complementation data, the expression of the Drosophila 
topoisomerase II gene in yeast cells with a disruption in TOP2 can also be 
detected by immunochemical methods with an antibody specific for Drosophila 
topoisomerase II.