1. ZHOU, B.S., BASTOW, K.F. AND CHENG, Y.C.
Characterization of the 3' region of the human DNA topoisomerase I gene.
CANCER RES. 49 3922-3927 (1989).
2. TAMURA, H., KOHCHI, C., YAMADA, R., IKEDA, T., KOIWAI, O., PATTERSON,
E., KEENE, J.D., OKADA, K., KJELDSEN, E. AND NISHIKAWA, K.
Molecular cloning of a cDNA of a camptothecin-resistant human DNA
topoisomerase I and identification of mutation sites.
NUCLEIC ACIDS RES. 19 69-75 (1991).
Eukaryotic topoisomerase I, otherwise known as relaxing enzyme, untwisting
enzyme or swivelase, catalyses the ATP-independent breakage of single-
stranded DNA, followed by passage and rejoining of another single-stranded
DNA region . This reaction brings about the conversion of one topological
DNA isomer into another: e.g., relaxation of positive and negative super-
coils; interconversion of simple and knotted rings of single-stranded DNA;
and intertwisting of single-stranded rings of complementary sequences [1,2].
A tyrosine residue at the active site is involved in the transient breakage
of a DNA strand and formation of a covalent protein-DNA intermediate .
Human topoisomerase I has been shown to be inhibited by camptothecin (CPT),
a plant alkaloid with antitumour activity .
EUTPISMRASEI is a 6-element fingerprint that provides a signature for
eukaryotic topoisomerase I. The fingerprint was derived from an initial
alignment of 7 sequences: the motifs were drawn from conserved regions
throughout the alignment length - motif 6 contains part of the region
encoded by PROSITE pattern TOPOISOMERASE_I_EUK (PS00176), the tyrosine
residue of which is involved in creating the covalent protein-DNA
intermediate. Two iterations on OWL26.3 were required to reach convergence,
at which point a true set comprising 16 sequences was identified.
An update on SPTR37_9f identified a true set of 28 sequences, and 6