期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 99, 期 26, 页码 17203-17208出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.262578499
关键词
DnaB; RecA; cyanobacteria; Synechococcus
资金
- NIGMS NIH HHS [GM32335, R01 GM032335, U01 GM032335] Funding Source: Medline
- NIMH NIH HHS [K02 MH001179, MH43836, MH01179, R01 MH043836] Funding Source: Medline
KaiC from Synechococcus elongatus PCC 7942 (KaiC) is an essential circadian clock protein in cyanobacteria. Previous sequence analyses suggested its inclusion in the RecA/DnaB superfamily. A characteristic of the proteins of this superfamily is that they form homohexameric complexes that bind DNA. We show here that KaiC also forms ring complexes with a central pore that can be visualized by electron microscopy. A combination of analytical ultracentrifugation and chromatographic analyses demonstrates that these complexes are hexameric. The association of KaiC molecules into hexamers depends on the presence of ATP. The KaiC sequence does not include the obvious DNA-binding motifs found in RecA or DnaB. Nevertheless, KaiC binds forked DNA substrates. These data support the inclusion of KaiC into the RecA/DnaB superfamily and have important implications for enzymatic activity of KaiC in the circadian clock mechanism that regulates global changes in gene expression patterns.
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