SYNTHESIS OF THE CAULOBACTER FERREDOXIN PROTEIN, FDXA, IS CELL-CYCLE CONTROLLED

The fdxA gene was identified upstream of and in the opposite direction from the Caulobacter crescentus cysC gene. Analyses of the nucleotide sequence and the deduced amino acid sequence of the fdxA gene demonst rated that it encodes a ferredoxin with a molecular mass of 12,080 Da. This ferredoxin has common structural features with ferredoxins that contain a [3Fe-4S] and a [4Fe-4S] cluster, including seven conserved c ysteines responsible for the binding of the two clusters. A mutation i n the fdxA gene was obtained, and the resulting strain did not produce one of the two ferredoxins (FdI) found in C. crescentus. Further expe riments demonstrated that the fdxA gene is temporally expressed in C. crescentus and that FdI is required for completion of the cell cycle a t 37 degrees C.