Expression and regulation pattern of ferritin-like DpsA in the Archaeon Halobacterium salinarum

Very recently, an iron-rich protein, DpsA, was isolated from the extreme halophilic euryarchaeon Halobacterium salinarum JW5 and characterized. The amino acid sequence of DpsA is related to Dps proteins which belong structurally to the ferritin superfamily but differ from ferritins in their function and regulation. Employing Northern and Western blot analysis, the expression of DpsA in H. salinarum was examined throughout all growth phases and under a variety of growth conditions (iron deficiency, iron supplied growth, oxidative stress). DpsA shows increasing expression of dpsA mRNA in iron-rich media and under conditions of oxidative stress (H₂O₂), whereas under iron-deficient conditions mRNA-levels decrease. This is in contrast to Dps-type proteins the transcription of which is induced under conditions of iron starvation. Northern blot experiments show that the expression pattern of halobacterial DpsA is the same as that found in the few bacterial non-heme ferritin the expression pattern of which has been analyzed so far. Based on Western-blot analysis post-transcriptional regulation, typical of mammalian ferritins, can be excluded. This protein exhibits features of a non-heme type bacterial ferritin although it shares only little sequence similarity with Ftn from E. coli.