The 165-kDa DNA topoisomerase I from Xenopus laevis oocytes is a tissue-specific variant.
Two forms of topoisomerase I can be purified from Xenopus laevis. A protein with a molecular mass of 165 kDa has been identified as topoisomerase I in ovaries (Richard and Bogenhagen, 1989. J. Biol. Chem. 264, 4704-4709). When a similar purification is performed using liver tissue, topoisomerase I is purified as a 110-kDa protein. Separate rabbit antisera were raised against oocyte and liver topoisomerase I polypeptides. Each antiserum reacts in immunoblotting or immunoprecipitation procedures only with the tissue-specific topoisomerase I polypeptide against which it was generated. The failure of the antiserum raised against liver topoisomerase I to cross-react with the oocyte enzyme suggests that the smaller topoisomerase I is not derived from the 165-kDa oocyte enzyme by proteolysis. X. laevis tissue culture cells lysed and processed in the presence of SDS contain the 110-kDa form of topoisomerase I. The 165-kDa form of topoisomerase I disappears during oocyte maturation in vitro.
Richard
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Department of Pharmacological Sciences, State University of New York, Stony Brook 11794.
Bogenhagen
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D000818:Animals; D046508:Culture Techniques; D004264:DNA Topoisomerases, Type I / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D007106:Immune Sera; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D009865:Oocytes / Q000201:enzymology* / Q000502:physiology; D009928:Organ Specificity; D010053:Ovary / Q000196:embryology / Q000201:enzymology*; D011817:Rabbits; D014982:Xenopus laevis
D007106:Immune Sera; D004264:DNA Topoisomerases, Type I