These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: A catalytic domain of eukaryotic DNA topoisomerase I.
    Author: Cheng C, Shuman S.
    Journal: J Biol Chem; 1998 May 08; 273(19):11589-95. PubMed ID: 9565576.
    Abstract:
    Eukaryotic type IB topoisomerases catalyze the cleavage and rejoining of DNA strands through a DNA-(3'-phosphotyrosyl)-enzyme intermediate. The 314-amino acid vaccinia topoisomerase is the smallest member of this family and is distinguished from its cellular counterparts by its specificity for cleavage at the target sequence 5'-CCCTT downward arrow. Here we show that Topo-(81-314), a truncated derivative that lacks the N-terminal domain, performs the same repertoire of reactions as the full-sized topoisomerase: relaxation of supercoiled DNA, site-specific DNA transesterification, and DNA strand transfer. Elimination of the N-terminal domain slows the rate of single-turnover DNA cleavage by 10(-3.6), but has little effect on the rate of single-turnover DNA religation. DNA relaxation and strand cleavage by Topo-(81-314) are inhibited by salt and magnesium; these effects are indicative of reduced affinity in noncovalent DNA binding. We report that identical properties are displayed by a full-length mutant protein, Topo(Y70A/Y72A), which lacks two tyrosine side chains within the N-terminal domain that contact the DNA target site in the major groove. We speculate that Topo-(81-314) is fully competent for transesterification chemistry, but is compromised with respect to a rate-limiting precleavage conformational step that is contingent on DNA contacts made by Tyr-70 and Tyr-72.
    [Abstract] [Full Text] [Related] [New Search]