X-linked hypophosphatemic rickets (HYP) is a dominant disorder characterised by impaired phosphate uptake in the kidney, which is likely to be caused by abnormal regulation of sodium phosphate cotransport in the proximal tubules. By positional cloning, we have isolated a candidate gene from the HYP region in Xp22.1. This gene exhibits homology to a family of endopeptidase genes, members of which are involved in the degradation or activation of a variety of peptide hormones. This gene (which we have called PEX) is composed of multiple exons which span at least five cosmids. Intragenic non-overlapping deletions from four different families and three mutations (two splice sites and one frameshift) have been detected in HYP patients, which suggest that the PEX gene is involved in the HYP disorder.

We analyzed the metabolic rhythms and differential gene expression in the unicellular, diazotrophic cyanobacterium Cyanothece sp. strain ATCC 51142 under N 2 -fixing conditions after a shift from normal 12-h light-12-h dark cycles to continuous light. We found that the mRNA levels of ϳ10% of the genes in the genome demonstrated circadian behavior during growth in free-running (continuous light) conditions. The genes for N 2 fixation displayed a strong circadian behavior, whereas photosynthesis and respiration genes were not as tightly regulated. One of our main objectives was to determine the strategies used by these cells to perform N 2 fixation under normal day-night conditions, as well as under the greater stress caused by continuous light. We determined that N 2 fixation cycled in continuous light but with a lower N 2 fixation activity. Glycogen degradation, respiration, and photosynthesis were also lower; nonetheless, O 2 evolution was about 50% of the normal peak. We also demonstrated that nifH (encoding the nitrogenase Fe protein), nifB, and nifX were strongly induced in continuous light; this is consistent with the role of these proteins during the assembly of the enzyme complex and suggested that the decreased N 2 fixation activity was due to protein-level regulation or inhibition. Many soluble electron carriers (e.g., ferredoxins), as well as redox carriers (e.g., thioredoxin and glutathione), were strongly induced during N 2 fixation in continuous light. We suggest that these carriers are required to enhance cyclic electron transport and phosphorylation for energy production and to maintain appropriate redox levels in the presence of elevated O 2 , respectively.

In this article, we demonstrate the connection between intracellular iron storage and oxidative stress response in cyanobacteria. Iron is essential for the survival of all organisms. However, the redox properties that make iron a valuable cofactor also lead to oxidative interactions, resulting in the formation of harmful radicals. Therefore, iron accumulation in cells should be tightly regulated, a process in which ferritin family proteins play an important role. Synechocystis sp. PCC 6803 contains two ferritintype storage complexes, bacterioferritin and MrgA. Previous studies demonstrated the role of bacterioferritin and MrgA in iron storage. In addition, MrgA was found to play a key role in oxidative stress response. Here, we examined the dual role of the ferritin family proteins using physiological and transcriptomic approaches. Microarray analysis of iron-limited wild-type and DmrgA cultures revealed a substantial up-regulation of oxidative stress-related genes in mutant cells. The PerR regulator was found to play an important role in that process. Furthermore, we were able to demonstrate the connection between internal iron quota, the presence of the two storage complexes, and the sensitivity to externally applied oxidative stress. These data suggest a pivotal role for the ferritin-type proteins of Synechocystis sp. PCC 6803 in coordinating iron homeostasis and in oxidative stress response. The combined action of the two complexes allows for the safe accumulation and release of iron from storage by minimizing damage resulting from interactions between reduced iron and the oxygen radicals that are produced in abundance by the photosynthetic apparatus.