SMALL ANGLE X-RAY SCATTERING OF CIRCADIAN CLOCK PROTEIN COMPLEX

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Circadian clocks are self-sustained biochemical oscillators. Their properties include temperature compensation, a time constant of approximately 24 hr, and high precision (Dunlap et al., 2004). These properties are difficult to explain by known biochemical reactions. The ultimate explanation for the mechanism of these unusual oscillators will require characterizing the structures, functions, and interactions of the molecular components of circadian clocks. We propose to understand the components of the biological clock in the prokaryotic cyanobacteria, where genetic/biochemical studies have been productive (Ishiura et al. 1998, Nakahira et al. 2004 and Johnson2004). An intriguing feature of the circadian clock system of cyanobacteria is that of global gene regulation-essentially all the promoters in the organism are under circadian control. Even heterologous promoters are expressed rhythmically introduced into cyanobacteria (Nakahira et al. 2004). A mutational analysis discovered that this system is regulated by at least three essential clock genes, kaiA, kaiB, and kaiC, that form a cluster on the chromosome (Ishiura et al., 1998). The proteins encoded by these genes interact with each other (Iwasaki et al. 1999 and Taniguchi et al. 2001) to form large complexes in vivo in which KaiC is the hexameric core. The crystal structure of the KaiC (Pattanayek et al., 2003),KaiA and KaiB are known by different groups. We propose to analyze interactions among the clock proteins KaiA, KaiB, and KaiC in solution through small angle X-ray scattering.