Structural similarities between M. luteus and E. coli DNA topoisomerase I

Type I DNA topoisomerase has been isolated from Micrococcus luteus following a procedure that takes advantage of the binding of the enzyme to heparin and single stranded DNA. Almost pure enzyme was obtained using two successive affinity chromatography steps: on heparin Sepharose and ssDNA cellulose. The method was rapid and allowed the isolation of DNA topoisomerase I from M. luteus in mg quantities. Polyclonal antibodies raised in rabbit were shown to cross-react with type I DNA topoisomerase of Escherichia coli. Partial protein sequencing of the M. luteus enzyme identified a peptide with high similarity to the putative protein sequence of E. coli DNA topoisomerase I, aligning with 73% identity to amino acids 491-505.