Abstract
Sulfite redutase (SiR) is encoded by the nuclear genome in plants and located in the plastid stroma. Previous studies demonstrated that SiR is also a major component of pea plastid nucleoids. Although plastid DNA originates from cyanobacterial genome, it is unclear if the SiR homologue is a component of cyanobacterial nucleoids. In the present study, we investigated the DNA binding properties of the SiR of the cyanobacterium Anabaena sp. PCC 7120 and the unicellular red alga Cyanidioschyzon merolae. The SiR protein fused with GST and histidine-tag was expressed in E. coli and purified. Co-expression with siroheme synthase increased the yield of SiR. The presence of the prosthetic group was confirmed by UV absorption measurement. The antibody against SiR was produced, and SiR was detected in the algal nucleoids by immunoblotting. Mixture of SiR and plastid DNA was examined with a fluorescence microscope, and small particles were observed.
