KaiB is a component of the circadian clock molecular machinery in cyanobacteria, which are the simplest organisms that exhibit circadian rhythms. Here we report the x-ray crystal structure of KaiB from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. The KaiB crystal diffracts at a resolution of 2.6 Å and includes four subunits organized as a dimer of dimers, each composed of two non-equivalent subunits. The overall shape of the tetramer is an elongated hexagonal plate, with a single positively charged cleft flanked by two negatively charged ridges whose surfaces includes several terminal chains. Site-directed mutagenesis of Synechococcus KaiB confirmed that alanine substitution of residues Lys-11 or Lys-43 in the cleft, or deletion of C-terminal residues 95-108, which forms part of the ridges, strongly weakens in vivo circadian rhythms. Characteristics of KaiB deduced from the x-ray crystal structure were also confirmed by physicochemical measurements of KaiB in solution. These data suggest that the positively charged cleft and flanking negatively charged ridges in KaiB are essential for the biological function of KaiB in the circadian molecular machinery in cyanobacteria.

Background:The function of KaiB remains to be solved. Results: Dimeric KaiB 1-94 generated circadian oscillation in vitro, but it did not in cells. Conclusion: KaiB tetramer-dimer transformation is responsible for the regulation of the SasA-mediated clock output pathway. Significance: We demonstrated the role of KaiB in the regulation of the SasA-KaiC interaction, involved in the transmission of time-information from KaiABC-machinery to transcription apparatus.

It has recently been shown that an insertion (I)/deletion (D) polymorphism exists in the angiotensin-converting enzyme (ACE) gene, and that this polymorphism affects the serum ACE level. There are three genotypes: DD, DI, and II, with the ACE level highest in DD, intermediate in DI, and lowest in II. In the present investigation of the possible significance of the polymorphism for sarcoidosis, a total of 207 patients and 314 normal control subjects were examined. There were no significant differences in the I/D ratio and the genotype distribution between the two groups, and no significant variation in organ involvement (i.e., eye, skin, and heart) was noted among the three genotypes. To determine any prognostic influence of the polymorphism, we examined the disappearance ratio of abnormal shadow on chest radiography over 3 and 5 yr. No significant difference among the three genotypes was observed. New normal ranges of serum ACE level were determined for each genotype, and found to be 22% more sensitive overall than the conventional normal range and 39% more so for II type, suggesting an advantage for diagnosis and assessment of the disease activity of sarcoidosis.

Na؉ /H ؉ antiporters influence proton or sodium motive force across the membrane. Synechocystis sp. PCC 6803 has six genes encoding Na ؉ /H؉ antiporters, nhaS1-5 and sll0556. In this study, the function of NhaS3 was examined. NhaS3 was essential for growth of Synechocystis, and loss of nhaS3 was not complemented by expression of the Escherichia coli Na ؉ /H ؉ antiporter NhaA. Membrane fractionation followed by immunoblotting as well as immunogold labeling revealed that NhaS3 was localized in the thylakoid membrane of Synechocystis. NhaS3 was shown to be functional over a pH range from pH 6.5 to 9.0 when expressed in E. coli. A reduction in the copy number of nhaS3 in the Synechocystis genome rendered the cells more sensitive to high Na ؉ concentrations. NhaS3 had no K ؉ /H ؉ exchange activity itself but enhanced K ؉ uptake from the medium when expressed in an E. coli potassium uptake mutant. Expression of nhaS3 increased after shifting from low CO 2 to high CO 2 conditions. Expression of nhaS3 was also found to be controlled by the circadian rhythm. Gene expression peaked at the beginning of subjective night. This coincided with the time of the lowest rate of CO 2 consumption caused by the ceasing of O 2 -evolving photosynthesis. This is the first report of a Na