Abstract
It has been reported that in bacteria, such as Azotobacter vinelandii, several factors are involved in the assembling of iron-sulfur cluster. The genes encoding these factors constitute iscSUA-hscBA-fdx cluster on the genome. Green sulfur bacterium Chlorobium tepidum, an anaerobic photosynthetic bacterium, has an iron-sulfur type reaction center and nitrogenase for nitrogen-fixation. In the whole genome of C. tepidum, homologues of iscU (CT1994) and iscS (CT1995) are found. In A. vinelandii, another gene nifU is involved in assembling of nitrogenase, homologue of nifU C-terminal domain (CT1786) is also found in the genome of C. tepidum. To investigate the mechanism of iron-sulfur cluster assembly in C. tepidum, we constructed recombinant IscU (CT1994), IscS (CT1995), truncate form of IscU and NifU homolog (CT1786) and over-expressed in E. coli. Absorption spectra and cryogenic ESR spectra suggested that the purified IscU binds [2Fe-2S] cluster.
