Sll0939 is induced by Slr0967 in the cyanobacterium Synechocystis sp. PCC6803 and is essential for growth under various stress conditions.

In this study, the genes expressed in response to low pH stress were identified in the unicellular cyanobacterium Synechocystis sp. PCC 6803 using DNA microarrays. The expression of slr0967 and sll0939 constantly increased throughout 4-h acid stress conditions. Overexpression of these two genes under the control of the trc promoter induced the cells to become tolerant to acid stress. The Δslr0967 and Δsll0939 mutant cells exhibited sensitivity to osmotic and salt stress, whereas the trc mutants of these genes exhibited tolerance to these types of stress. Microarray analysis of the Δslr0967 mutant under acid stress conditions showed that expression of the high light-inducible protein ssr2595 (HliB) and the two-component response regulator slr1214 (rre15) were out of regulation due to gene inactivation, whereas they were upregulated by acid stress in the wild-type cells. Microarray analysis and real-time quantitative reverse transcription-polymerase chain reaction analysis showed that the expression of sll0939 was significantly repressed in the slr0967 deletion mutant. These results suggest that sll0939 is directly involved in the low pH tolerance of Synechocystis sp. PCC 6803 and that slr0967 may be essential for the induction of acid stress-responsive genes.

Slr0967 and Sll0939 induced by the SphR response regulator in Synechocystis sp. PCC 6803 are essential for growth under acid stress conditions.

Two-component signal transduction is the primary signaling mechanism for global regulation of the cellular response to environmental changes. We used DNA microarray analysis to identify genes that were upregulated by acid stress in the cyanobacterium Synechocystis sp. PCC 6803. Several of these genes may be response regulators that are directly involved in this type of stress response. We constructed deletion mutants for the response regulator genes and compared the growth rates of cells transfected with mutant and wild-type genes in a low pH medium. Of these mutants, deletion of sphR affected the growth rate under acid stress (pH 6.0) conditions. We examined genome-wide expression in ΔsphR mutant cells using DNA microarray to determine whether SphR was involved in the regulation of other acid stress responsive genes. Microarray and real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analyses of wild-type cells showed that the expression of phoA, pstS1, and pstS2, which are upregulated under phosphate-limiting conditions, increased (2.48-, 1.88-, and 5.07-fold, respectively) after acid stress treatment for 0.5h. In contrast, pstS2 expression did not increase in the ΔsphR mutant cells after acid stress, whereas the phoA and sphX mRNA levels increased. Furthermore, qRT-PCR and northern blot analysis indicated that downregulation of the acid-responsive genes slr0967 and sll0939 occurred with the deletion of sphR. Indeed, mutants of these genes were more sensitive to acid stress than the wild-type cells. Thus, induction of Slr0967 and Sll0939 by SphR may be essential for growth under acid stress conditions. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

High-dose interferon-alpha therapy lowers the levels of serum fibrogenesis markers over 5 years in chronic hepatitis C.

We examined the levels of serum N-terminal peptide of type III procollagen (P-III-NP) and the 7S domain of type IV collagen (IV-7S) as fibrogenesis markers in patients with chronic hepatitis C to clarify whether high-dose interferon-alpha (IFN-alpha) therapy has a suppressive effect on hepatic fibrogenesis for a long period (over 5 years) after the cessation of IFN therapy. Eighty patients with CHC were given 10 million units of IFN-alpha2b daily for 14 days followed by three times per week for a total of 24 weeks. Patients were divided into the following three groups according to the highest serum alanine aminotransferase levels during 1 year observation after the end of IFN therapy: complete responders (CR), partial responders (PR), and nonresponders (NR). We measured serum fibrogenesis markers before and at the end of IFN therapy, and again 1 year and more than 5 years after the end of IFN therapy. Liver biopsies were performed before IFN therapy in all patients and again over long-term observation in 10 patients (PR; 5 and NR; 5). Serum P-III-NP levels significantly decreased after IFN therapy in all three groups of patients, and further decreased in CR and PR over long-term observation. Serum IV-7S levels in CR significantly decreased after IFN therapy and further decreased over long-term observation. Serum IV-7S levels over long-term observation were significantly lower than those at the end of IFN therapy in CR and PR and significantly lower than the initial values in all three groups of patients. The progression of fibrosis was not significant over long-term observation in liver biopsy specimens of 10 patients. The results of the present study suggest that high-dose IFN-alpha therapy for 6 months suppresses the progression of hepatic fibrosis for more than 5 years not only in CR but also in PR.