Isolation and nucleotide sequence analysis of the ferredoxin I gene from the cyanobacterium Anacystis nidulans R2

Two mixed oligonucleotide probes derived from conserved regions of the Synechocystis sp. strain PCC 6714 ferredoxin amino acid sequence were utilized to isolate an Anacystis nidulans R2 clone containing the ferredoxin I gene. Nucleotide sequence analysis revealed a 297-base-pair (bp) open reading frame with a deduced amino acid sequence having high homology to other cyanobacterial ferredoxins. Assuming proteolytic cleavage of the initial methionine residue, the molecular weight of the mature A. nidulans R2 ferredoxin was 10,370. The initial methionine residue was preceded by a probable ribosome-binding site sequence, AGGA. Northern hybridization analysis with the cloned ferredoxin gene indicated an RNA transcript of approximately 450 bp. S1 nuclease mapping localized the transcription start site to a position 64 bases upstream from the initial methionine residue. The nucleotide sequence 14 to 8 bp preceding the transcription start site resembled a typical Escherichia coli promoter, but the sequence in the -35 region did not. Southern hybridization detected only a single copy of the ferredoxin sequence in the A. nidulans R2 genome.