HUMAN TOP3 - A SINGLE-COPY GENE ENCODING DNA TOPOISOMERASE-III

A human cDNA encoding a protein homologous to the Escherichia coli DNA topoisomerase I subfamily of enzymes has been identified through clon ing and sequencing, Expressing the cloned human cDNA in yeast Delta to p1 cells lacking endogenous DNA topoisomerase I yielded an activity in cell extracts that specifically reduces the number of supercoils in a highly negatively supercoiled DNA, On the basis of these results, the human gene containing the cDNA sequence has been denoted TOP3, and th e protein it encodes has been denoted DNA topoisomerase III. Screening of a panel of human-rodent somatic hybrids and fluorescence in situ h ybridization of cloned TOP3 genomic DNA to metaphase chromosomes indic ate that human TOP3 is a single-copy gene located at chromosome 17p11. 2-12.