title: cDNA cloning of human DNA topoisomerase I: catalytic activity of a 67.7-kDa carboxyl-terminal fragment.
abstract: cDNA clones encoding human topoisomerase I were isolated from an expression vector library (lambda gt11) screened with autoimmune anti-topoisomerase I serum. One of these clones has been expressed as a fusion protein comprised of a 32-kDa fragment of the bacterial TrpE protein linked to 67.7 kDa of protein encoded by the cDNA. Three lines of evidence indicate that the cloned cDNA encodes topoisomerase I. (i) Proteolysis maps of the fusion protein and human nuclear topoisomerase I are essentially identical. (ii) The fusion protein relaxes supercoiled DNA, an activity that can be immunoprecipitated by anti-topoisomerase I serum. (iii) Sequence analysis has revealed that the longest cDNA clone (3645 base pairs) encodes a protein of 765 amino acids that shares 42% identity with Saccharomyces cerevisiae topoisomerase I. The sequence data also show that the catalytically active 67.7-kDa fragment is comprised of the carboxyl terminus.
authors.affiliation: Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: P
authors.initials: P
authors.lastname: D'Arpa
authors.forename: P S
authors.initials: PS
authors.lastname: Machlin
authors.forename: H
authors.initials: H
authors.lastname: Ratrie
authors.forename: N F
authors.initials: NF
authors.lastname: Rothfield
authors.forename: D W
authors.initials: DW
authors.lastname: Cleveland
authors.forename: W C
authors.initials: WC
authors.lastname: Earnshaw
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D004264:DNA Topoisomerases, Type I / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007158:Immunologic Techniques; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis
chemical_list: D010446:Peptide Fragments; D004247:DNA; D004264:DNA Topoisomerases, Type I