Localization of a high molecular weight form of DNA topoisomerase I in amphibian oocytes.
Xenopus oocytes express a 165 kDa variant of DNA topoisomerase I (topo I) as opposed to the canonical 110 kDa form of somatic cells (Richard and Bogenhagen, Dev. Biol. 146: 4-11, 1991). By immunofluorescence microscopy using variant-specific antibodies we show that this high molecular weight form is associated with lampbrush chromosome loops and the inner regions of the amplified nucleoli. Inhibition of topo I-activity by either Camptothecin-treatment or microinjection of neutralizing antibodies resulted in loop retraction and the condensation of chromosomes and amplified nucleoli. These data indicate that the oocyte-specific 165 kDa form of topo I is involved in transcriptional processes mediated by RNA polymerase I and II and is therefore functionally equivalent to the somatic cell 110 kDa counterpart.
Gebauer
D
D
Department of Cell and Developmental Biology, Theodor-Boveri-Institute (Biocenter), University of Würzburg, Germany.
Mais
C
C
Zinger
K
K
Hock
R
R
Lieb
B
B
Scheer
U
U
D000818:Animals; D002466:Cell Nucleolus / Q000201:enzymology; D002875:Chromosomes / Q000201:enzymology; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D005260:Female; D008856:Microscopy, Fluorescence; D008970:Molecular Weight; D009865:Oocytes / Q000201:enzymology*; D014982:Xenopus laevis / Q000378:metabolism*
D004264:DNA Topoisomerases, Type I