Volume 1

Contemporary classics in the life sciences / edited by James T. Barrett.

Date:
[1986-]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Contemporary classics in the life sciences / edited by James T. Barrett. Source: Wellcome Collection.

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    Tftfs week's Citation Classic Kellenberger E, Ryter A & Séchaud J. Electron microscope study of DNA-containing plasms. II. Vegetative and mature phage DNA as compared with normal bacterial nucleoids in different physiological states. J. Biophys. Biochem. Cytol. 4:671-8, 1958. [Laboratoire de Biophysique, University of Geneva, Geneva, Switzerland] Under specific conditions—later called the 'R.K.-conditions' — bacterial nucleoids can be fixed with 0s0 4 so as to contain fine fibrillar material when viewed on thin sec tions. Under other conditions, and —as was shown later —with aldehydes, aggregations occur. Those induced with EDTA (formerly under the trade name 'versene') allow a practical aggregation test. The pool of vegetative ( = replicating and transcribing) T4 bacteriophage DNA is shown to be aggre gation sensitive, as is the normal nucleoid. Artificial aggregation is different from physiological condensation as occurs, e.g., when T4-virions are packaged out of the DNA-pool. [The SC/® indicates that this paper has been cited over 915 times since 1961.] Edward Kellenberger Biozentrum der Universität Basel Abteilung Mikrobiologie CH-4056 Basel Klingelbergstrasse 70 Switzerland July 24, 1978 The initial idea of a series of papers —of which this was the second —was to establish a test for distinguishing condensed DNA- plasms of eukaryotes, e g , metaphase chro mosomes from metabolicallv active, non- condensed DNA, e.g., of DNA-plasms in the interphase of eukaryotes or during all times in prokaryotes At that time the possibility was still open that the histones condense the DNA and render it thus metabolically inert By removal of histones a decondensed DNA-plasm would arise which would be metabolically active The decondensed DNA-plasms of bacterial nuclei and vegetative phage were known to be con tinuously replicating and transcribing Some experiments then suggested that bacteria have no histones and in general fewer pro teins bound to their DNA My working hypothesis at that time was thus that during interphase the DNA-plasm of eukaryotes might be organised similar to that of pro karyotes; only the condensed metaphase chromosomes would have been specific for eukaryotes The later applications of the methodol ogy of this paper by others and ourselves showed that the DNA-plasms of mitochon dria, chloroplasts, blue-green algae, dinoflagellates, and kinetoplasts of trypanosoma had a structure and behavior in fixation (coagulation-sensitive) analogous to that of bacteria The DNA-plasm of inter phase nuclei of eukaryotes, however, turned out not to be coagulation-sensitive It also did not have the same fibrillar aspect. This result was suspected to be in relation to DNA binding proteins but only with our present knowledge can we understand it: in eukaryotes most of the histones always stay associated with the DNA of the chromatin For bacteria, DNA binding proteins (dif ferent from histones) are demonstrated, but they are still found only in amounts which lead to much smaller protein-DNA ratios as in eukaryotes. Hence, it would be under standable that prokaryotic DNA-plasms behave similarly to naked DNA, while chromatin does not Although we intended to draw the atten tion of the reader to the different organisa tional states of the nuclear material and how it can efficiently be investigated by electron microscopy of thin sections, I believe that the paper is mostly quoted as reference for a certain condition of fixation, which is mainly the result of an enormous effort of my collaborator Antoinette Ryter, then technician, now research director at the Pasteur Institute in Paris It is only now, after the nucleosomes have been described, that some people are becoming aware again of possible differences between the prokary otic and the eukaryotic type of organisation of the nuclear material Others do not like differences and seize anything which could appear as evidence that bacterial DNA is organised with the same 'beads' as is the chromatin of eukaryotes Has it not been demonstrated that SV40 virus is constructed by way of nucleosomes' As for most people viruses are lower organisms than bacteria, do we not have to expect nucleosomes also in bacteria? This wishful thinking reminds me of earlier times, when it became clear that microorganisms have genetics and when people thus tried very hard to demon strate spindles and centrosomes in bacteria 1 Hopefully, further thorough investigation of bacterial chromosomes will not be inhibited by preconceptions and soon an explanation of the above discussed fundamental dif ference of prokaryotic and eukaryotic DNA- plasms will be provided
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