Biomedical subjects

Cécile Pasternak

Publications and source records attributed to Cécile Pasternak.

3 recordsLinked to original sources

PubMed2004

Thioredoxin can influence gene expression by affecting gyrase activity.

The expression of many genes of facultatively photosynthetic bacteria of the genus Rhodobacter is controlled by the oxygen tension. Among these are the genes of the puf and puc operons, which encode proteins of the photosynthetic apparatus. Previous results revealed that thioredoxins are involved in the regulated expression of these operons, but it remained unsolved as to the mechanisms by which thioredoxins affect puf and puc expression. Here we show that reduced TrxA of Rhodobacter capsulatus and Rhodobacter sphaeroides and oxidized TrxC of R.capsulatus interact with DNA gyrase and alter its DNA supercoiling activity. While TrxA enhances supercoiling, TrxC exerts a negative effect on this activity. Furthermore, inhibition of gyrase activity strongly reduces puf and puc expression. Our results reveal a new signaling pathway by which oxygen can affect the expression of bacterial genes.

Bacterial Proteins↗

PubMed2003

Expression of the trxA gene for thioredoxin 1 in Rhodobacter sphaeroides during oxidative stress.

Expression of the thioredoxin ( trxA) gene of Rhodobacter sphaeroides is regulated by oxidative stress at the transcriptional and post-transcriptional levels. All oxidative stress agents tested resulted in a moderate or strong increase of trxA mRNA levels, which was not due to increased mRNA stability. While the kinetics of increased trxA mRNA and of sodB mRNA, encoding superoxide dismutase, were similar after addition of tert-butyl hydroperoxide ( t-BOOH) or hydrogen peroxide (H(2)O(2)), different kinetics were observed after addition of diamide or paraquat, indicating the involvement of different stress responses in the regulation of these genes. The level of TrxA did not increase to the same extent as trxA mRNA levels. Furthermore, the addition of H(2)O(2) or t-BOOH led to increased turnover of the protein. Apparently, increased txA transcription compensated, at least in part, for the reduced stability of the protein. A strain expressing lower levels of thioredoxin 1 showed decreased resistance to diamide and H(2)O(2) but increased resistance to paraquat and t-BOOH compared to the wild-type. These data implicate the involvement of various systems in the response to different types of oxidative stress and the participation of thioredoxin 1 in the defense against oxidative stress caused by diamide or H(2)O(2).

Bacterial Proteins↗

PubMed1997

Thioredoxin is essential for Rhodobacter sphaeroides growth by aerobic and anaerobic respiration.

To investigate the biological role of thioredoxin in the facultative photosynthetic bacterium Rhodobacter sphaeroides, attempts were made to construct a thioredoxin-deficient mutant by site-specific mutagenesis, using the Tn903 kanamycin resistance gene for selection. In situ and Southern hybridization analyses have demonstrated that the TrxA- mutation is lethal for R. sphaeroides growth under anaerobic conditions with DMSO as terminal electron acceptor and under aerobic conditions. In addition, the DNA region upstream of the trxA initiation codon is essential for aerobic growth of R. sphaeroides. An ORF of unknown function was identified in this region and is suggested to encode a product essential for aerobic metabolism of R. sphaeroides. The mechanism of thioredoxin action was also analysed by using the procedure for gene replacement to introduce a Cys33 to Ser mutation into the trxA chromosomal copy. The strain carrying this mutation produced a thioredoxin impaired in its protein-disulfide reductase activity and was also not viable. These data suggest that the physiological function of R. sphaeroides thioredoxin is redox-dependent. Thioredoxin purified from R. sphaeroides was shown to have a glutathione-disulfide oxidoreductase activity typical of glutaredoxins. This unexpected finding suggests that R. sphaeroides thioredoxin, in contrast to Escherichia coli thioredoxin, has the potential to act in GSH-dependent processes. Thus, the fundamental role of R. sphaeroides thioredoxin in cell growth probably originates from the multiple functions it can serve in vivo.

Aerobiosis↗