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Journal of Bacteriology, December 2001, p. 7260-7272, Vol. 183, No. 24
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.24.7260-7272.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Analysis of Transcription of the Staphylococcus aureus Aerobic Class Ib and Anaerobic Class III Ribonucleotide Reductase Genes in Response to Oxygen

Mahmud Masalha, Ilya Borovok, Rachel Schreiber, Yair Aharonowitz, and Gerald Cohen*

Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel

Received 3 July 2001/Accepted 19 September 2001

Staphylococcus aureus is a gram-positive facultative aerobe that can grow in the absence of oxygen by fermentation or by using an alternative electron acceptor. To investigate the mechanism by which S. aureus is able to adapt to changes in oxygen concentration, we analyzed the transcriptional regulation of genes that encode the aerobic class Ib and anaerobic class III ribonucleotide reductase (RNR) systems that are responsible for the synthesis of deoxyribonucleotides needed for DNA synthesis. The S. aureus class Ib RNR nrdIEF and class III RNR nrdDG genes and their regulatory regions were cloned and sequenced. Inactivation of the nrdDG genes showed that the class III RNR is essential for anaerobic growth. Inhibition of aerobic growth by hydroxyurea showed that the class Ib RNR is an oxygen-dependent enzyme. Northern blot analysis and primer extension analysis demonstrated that transcription of class III nrdDG genes is regulated by oxygen concentration and was at least 10-fold higher under anaerobic than under aerobic conditions. In contrast, no significant effect of oxygen concentration was found on the transcription of class Ib nrdIEF genes. Disruption or deletion of S. aureus nrdDG genes caused up to a fivefold increase in nrdDG and nrdIEF transcription under anaerobic conditions but not under aerobic conditions. Similarly, hydroxyurea, an inhibitor of the class I RNRs, resulted in increased transcription of class Ib and class III RNR genes under aerobic conditions. These findings establish that transcription of class Ib and class III RNR genes is upregulated under conditions that cause the depletion of deoxyribonucleotide. Promoter analysis of class Ib and class III RNR operons identified several inverted-repeat elements that may account for the transcriptional response of the nrdIEF and nrdDG genes to oxygen.

* Corresponding author. Mailing address: Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel, 69978. Phone: (972) 3 6409649. Fax: (972) 3 6409407. E-mail: coheng{at}post.tau.ac.il.

Journal of Bacteriology, December 2001, p. 7260-7272, Vol. 183, No. 24
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.24.7260-7272.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.