Interplay between formation of photosynthetic complexes and expression of genes for iron-sulfur cluster assembly inRhodobacter sphaeroides?

Formation of photosynthetic complexes leads to a higher demand for Fe-S clusters. We hypothesized that in the facultative phototrophic alpha-proteobacteriumRhodobacter sphaeroidesexpression of theisc-sufoperon for Fe-S cluster formation may be increased under conditions that promote formation of photosynthetic complexes and that, vice versa, lack of the IscR regulator may also affect photosynthesis gene expression. To test this hypothesis, we monitored the activities of theisc-sufsense and anti-sense promoters under different growth conditions and in mutants which are impaired in formation of photosynthetic complexes. We also tested expression of photosynthesis genes in a mutant lacking the IscR regulator. Our results are not in agreement with a co-regulation of the Isc-Suf system and the photosynthetic apparatus at level of transcription. We provide evidence that, coordination of the systems occurs at post-transcriptional levels. Increased levels ofisc-sufmRNAs under conditions promoting formation of photosynthetic complexes are due to higher RNA stability.

Automated summary

In Rhodobacter sphaeroides, under conditions promoting the formation of photosynthetic complexes, the increased levels of isc-suf mRNA are likely due to higher RNA stability rather than co-regulation at the transcriptional level. This indicates that in this bacterium, the Isc-Suf system and photosynthetic pigments are coordinated at post-transcriptional levels.