Cloning and characterization of the Aspergillus nidulans DNA topoisomerase I gene.

The topoisomerase I (TOP1) gene was cloned and sequenced from Aspergillus nidulans using the polymerase chain reaction (PCR). Genomic DNA was used as a template to obtain a 2987-bp gene containing five small introns. PCR from a cDNA library yielded a 2613-bp sequence which codes for an 871 amino acid protein. Comparison of the deduced amino acid sequence with other DNA topoisomerase I (topo I) protein sequences shows a somewhat higher degree of identity with other fungal amino acid sequences than with the human enzyme. Topo I is a ubiquitous enzyme which can be converted to a cytotoxic molecule in the presence of drugs that function as topo I poisons. The Aspergillus TOP1 cDNA will be used in an effort to identify novel cytotoxic antifungals which target this enzyme.