Drosophila DNA topoisomerase I is associated with transcriptionally active regions of the genome.

Abstract

The distribution of DNA topoisomerase I within Drosophila polytene chromosomes was observed by immunofluorescent staining with affinity-purified antibodies. The enzyme is preferentially associated with active loci, as shown by prominent staining of puffs. The heat shock loci 87A-87C are stained after, but not before, heat shock induction. A detailed comparison of the distribution of topoisomerase I with that of RNA polymerase II reveals a similar, al, though not identical, pattern of association. Topoisomerase I is also found in association with the nucleolus, the site of transcription by RNA polymerase I.The polytene chromosomes of the Drosophila salivary gland provide an excellent system for investigating the distribution of specific chromosomal proteins. Although highly organized, these giant chromosomes behave like diploid interphase chromatin in many assays of function and fine structure (1-6). They can, however, be easily observed under the light microscope; some substructure, such as transcriptionally active sites, can be recognized. It is possible to localize proteins in these chromosomes and thereby obtain some information as to the biological processes in which the given proteins might be involved. In order to visualize the chromosomal proteins, the method of indirect immunofluorescence was developed several years ago (7,8). The distribution patterns of a number of chromosomal proteins of unknown function have been determined by this approach (8-11). The method has allowed identification of a subclass of nonhistone chromosomal proteins that are prominently associated with loci that are active or inducible at some time in the salivary glands of the third instar larvae and prepupae (10,12,13).In addition, distribution patterns of proteins of known function have been analyzed-e.g., RNA polymerase 11 (14-17) and ribonucleoproteins (18). These proteins are preferentially associated with the transcriptionally active regions of the genome. In this paper we report the distribution pattern of DNA topoisomerase I. This enzyme is well characterized at the molecular level, but the range of its biological functions in eukaryotes has yet to be established (for reviews, see refs. 19-25). The ability of eukaryotic topoisomerase I to relax either negatively or positively supercoiled DNA hints that the enzyme might play a role in gene activation, either effecting structural changes in chromatin as it assumes a more "open" conformation (e.g., as detected by the appearance of puffs) and/or facilitating transcription per se (26, 27). There is some evidence in favor of a role of topoisomerase in transcription. For example, topoisomerase has been shown to be associated with ribosomal gene chromatin actively expressing rRNA (28); topoisomerase I is recovered with nucleosomes in a fraction enriched for transcriptionally active genes (29). Complex formation between eukaryotic DNA topoisomerase I and chromosomal high mobility group proteins and histone H1 has also been reported (30). However, there has been no direct evi...

First Results About Topoisomerase Activity in Astacus Astacus and Austropotamobius Pallipes as a Biomarker for Crayfish Viability

“…These results are not surprising since these are the ranges of temperatures considered physiological for the species. Moreover, these results are in agreement with the topoisomerase functions investigated in other invertebrates, such as Drosophila melanogaster, where topoisomerase I is actively involved in the transcription process of the adult (FLEISCHMANN et al, 1984;GILMOUR et al, 1986;GILMOUR and ELGIN, 1987) and during the developmental stages (ZHANG et al, 2000). No topoisomerase activity was found either in the spermiduct or in the muscle tissue at any of the tested temperatures.…”

Identification of a mammalian RNA polymerase I holoenzyme containing components of the DNA repair/replication system

“…In addition, TopoI co-localizes with RPI in immunohistochemical assays and co-purifies with RPI during biochemical purification of the enzyme (23,24). These observations suggest a specific role for TopoI in rDNA transcription.…”

Association of DNA topoisomerase I and RNA polymerase I: a possible role for topoisomerase I in ribosomal gene transcription

“…Immunoglobulins were purified by protein A-Sepharose chromatography. Monospecific antibodies were prepared by elution with 10 mM Hepes, pH 2.8 (Fleischmann et al 1984) from immunoblots of topoisomerase I.…”

“…Type I topoisomerase, first described in prokaryotes by Wang (1971) and in eukaryotes by Champoux and Dulbecco (1972) and later characterized by Keller (1975a, b), change the linking number in steps of one. Although their biological function is not completely defined , this class of topoisomerase has been implicated in transcriptional (Akrigg and Cook 1980;Dynan and Burgess 1981;Sternglanz et al 1981;Weisbrod 1982;Fleischmann et al 1984 ;Gilmour et al 1986;Shastry 1986) as well as in recombinational and replicational (Kikuchi and Nash 1979 ;Sternglanz et al 1981 ; also see Gellert 1981 ;Bullock et al 1985 ;Zeng et al 1985) events. J n higher eukaryotes topoisomerase I is enriched in the nucleolus (Fleischmann et al 1984;Muller et al 1985) and may play a role in transcription of supercoiled rDNA in vitro (Garg et al 1987).…”