A Caltech Library Service

Sequence Organization in Xenopus DNA Studied by the Electron Microscope

Chamberlin, Margaret E. and Britten, Roy J. and Davidson, Eric H. (1975) Sequence Organization in Xenopus DNA Studied by the Electron Microscope. Journal of Molecular Biology, 96 (2). pp. 317-333. ISSN 0022-2836.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


Xenopus laevis DNA was extracted from red blood cells and sheared to a mean length of 2780 nucleotides. The DNA was stripped of foldback-containing fragments and incubated to C_0t 10 (mol · s · l^(−1)), allowing most repetitive sequences to form duplex structures. Duplex-containing fragments were eluted from an hydroxylapatite column and visualized for electron microscopy by spreading from 57% formamide according to the modified Kleinschmidt technique of Davis et al. (1971). The mean length of the fragments observed was 2445 nucleotides. A total of 1700 DNA strands were photographed and studied. Less than 5% of the total strand length was in uninterpretable structures. Every molecule falling within the confines of the plates was included in the sample. Over 50% of the total strand length in the sample was found in structures bearing at least one interspersed repetitive sequence duplex terminated by four single-strand regions. The fraction of DNA present in duplex regions was almost exactly that predicted if the duplex regions represent all the interspersed middle repetitive sequence in the Xenopus genome. Direct measurement of visualized duplexes shows that the mean length of interspersed repetitive sequence elements in this genome is 345 nucleotides. Duplex length was shown to be independent of the length of the strands bearing the duplexes. These observations provide direct confirmation of the length of approximately 300 nucleotides indicated for interspersed repetitive sequences by earlier physical-chemical studies 011 Xenopus DNA. In strands carrying two duplexes terminated by single-strand regions the interduplex, or single-copy sequence element length could be measured. Sequence interspersion curves generated from these data are roughly consistent with those derived earlier from measurements of hydroxylapatite binding as a function of fragment length.

Item Type:Article
Related URLs:
URLURL TypeDescription
Additional Information:© 1975 Elsevier Ltd. Received 10 December 1974, Revised 30 April 1975. The authors acknowledge with pleasure the conscientious technical assistance of Mr Michael Kozlowski. We are grateful to Mr William R. Pearson, a graduate fellow of this Institute, for writing most of the computer programs used in this analysis. We wish to thank Drs Richard Deonier, Jerry Manning and Carl Schmid and Mr Mahlon "Wilkes for their assistance in learning the Kleinschmidt technique and Professor Norman Davidson of this Institute for his careful critical review of the manuscript. This research was supported by the National Institutes of Health (grant nos. HD05753 and GM20927) and by the National Science Foundation (grant no. GB33441X).
Funding AgencyGrant Number
Issue or Number:2
Record Number:CaltechAUTHORS:20160805-112703291
Persistent URL:
Official Citation:Margaret E. Chamberlin, Roy J. Britten, Eric H. Davidson, Sequence organization in Xenopus DNA studied by the electron microscope, Journal of Molecular Biology, Volume 96, Issue 2, 5 August 1975, Pages 317-324, IN5-IN7, 325-333, ISSN 0022-2836, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69476
Deposited By: Ruth Sustaita
Deposited On:05 Aug 2016 21:12
Last Modified:03 Oct 2019 10:22

Repository Staff Only: item control page