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J Bacteriol, April 1998, p. 2167-2174, Vol. 180, No. 8
Division of Biological Science, Graduate
School of Science, Nagoya University, Chikusa-ku, Nagoya 464-01, and National Institute for Basic Biology, Okazaki, Aichi 444, Japan
Received 8 December 1997/Accepted 17 February 1998
We cloned the pS1K1 plasmid in the process of apparently
"complementing" a circadian clock mutant of cyanobacterium
Synechococcus sp. strain PCC 7942, SP22, which has a 22-h
period (T. Kondo, N. F. Tsinoremas, S. S. Golden, C. H. Johnson, S. Kutsuna, and M. Ishiura, Science 266:1233-1236, 1994).
Sequence analysis revealed that SP22 did not have a
mutation in the genomic DNA segment carried on pS1K1, and the
sp22 mutation was later found in a recently cloned new
clock gene, kaiC. Therefore, the period-extender gene pex that was carried on pS1K1 was a suppressor gene for the
sp22 mutation. The pex gene encoded a protein
of 148 amino acid residues. No meaningful homologs were found in DNA or
protein databases including the Synechocystis genome
database. The pex gene was transcribed from 129 and 164 bp
upstream of the translation initiation codon as 0.6-kb transcripts. The
Pex protein was detected as a fusion protein with a molecular mass of
15 kDa by the epitope tag fusion method using a c-Myc epitope tag.
Disruption of the pex gene in wild-type cells shortened the
period of the rhythms by 1 h, although it did not affect other
properties of the rhythms, whereas its overexpression extended the
period by 3 h with a concomitant reduction in the amplitude of the
rhythms. In various clock mutants examined, overexpression caused
arrhythmicity. Thus, Pex is likely to function as a modifier of the
circadian clock in Synechococcus.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
A Period-Extender Gene, pex, That Extends the
Period of the Circadian Clock in the Cyanobacterium
Synechococcus sp. Strain PCC 7942
and
*
Corresponding author. Mailing address: Division of
Biological Science, Graduate School of Science, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya 464-01, Japan. Phone: 81-52-789-2507. Fax: 81-52-789-2963. E-mail: ishiura{at}bio.nagoya-u.ac.jp.
Present address: Division of Biological Informatics, Graduate
School of Human Informatics, Nagoya University, Chikusa-ku, Nagoya
464-01, Japan.
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