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Molecular and Cellular Biology, December 1998, p. 7235-7242, Vol. 18, No. 12
Department of Biochemistry and Molecular
Biology, University of Valencia, Burjassot, Valencia 46100, Spain1;
Department of Biology,
University of Oslo, Blindern, 0316 Oslo,
Norway2; and
The Biological
Laboratories, Harvard University, Cambridge, Massachusetts
021383
Received 19 May 1998/Returned for modification 14 July
1998/Accepted 28 August 1998
DNA supercoiling in the chloroplast of the unicellular green alga
Chlamydomonas reinhardtii was found to change with a
diurnal rhythm in cells growing in alternating 12-h dark-12-h light
periods. Highest and lowest DNA superhelicities occurred at the
beginning and towards the end of the 12-h light periods, respectively.
The fluctuations in DNA supercoiling occurred concurrently and in the
same direction in two separate parts of the chloroplast genome, one
containing the genes psaB, rbcL, and
atpA and the other containing the atpB gene.
Fluctuations were not confined to transcribed DNA regions, indicating
simultaneous changes in DNA conformation all over the chloroplast
genome. Because the diurnal fluctuations persisted in cells kept in
continuous light, DNA supercoiling is judged to be under endogenous
control. The endogenous fluctuations in chloroplast DNA topology
correlated tightly with the endogenous fluctuations of overall
chloroplast gene transcription and with those of the pool sizes of most
chloroplast transcripts analyzed. This result suggests that DNA
superhelical changes have a role in the regulation of chloroplast gene
expression in Chlamydomonas.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Endogenous Fluctuations of DNA Topology in the
Chloroplast of Chlamydomonas reinhardtii
*
Corresponding author. Mailing address: The Biological
Laboratories, Harvard University, 16 Divinity Ave., Cambridge, MA
02138. Phone: (617) 495-4292. Fax: (617) 495-4292. E-mail:
bogorad{at}biosun.harvard.edu.
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