Transcriptional regulation of the cydDC operon, encoding a heterodimeric ABC transporter required for assembly of cytochromes c and bd in Escherichia coli K-12: regulation by oxygen and alternative electron acceptors

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Abstract
The expression of the cydDC operon was investigated by using a chromosomal phi(cydD-lacZ) transcriptional fusion and primer extension analysis. A single transcriptional start site was found for cydD located 68 bp upstream of the translational start site, and Northern blot analysis confirmed that cydDC is transcribed as a polycistronic message independently of the upstream gene trxB. cydDC was highly expressed under aerobic growth conditions and during anaerobic growth with alternative electron acceptors. Aerobic expression was independent of ArcA and Fnr, but induction of cydDC by nitrate and nitrite was dependent on NarL and Fnr.