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Journal of Bacteriology, September 2009, p. 5622-5627, Vol. 191, No. 18
0021-9193/09/$08.00+0     doi:10.1128/JB.01716-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Identification and Characterization of Growth Suppressors of Escherichia coli Strains Lacking Phosphorolytic Ribonucleases{triangledown}

Chaitanya Jain*

Department of Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, Florida 33136

Received 8 December 2008/ Accepted 8 July 2009

RNases are involved in critical aspects of RNA metabolism in all organisms. Two classes of RNases that digest RNA from an end (exo-RNases) are known: RNases that use water as a nucleophile to catalyze RNA degradation (hydrolytic RNases) and RNases that use inorganic phosphate (phosphorolytic RNases). It has been shown previously that the absence of the two known Escherichia coli phosphorolytic RNases, polynucleotide phosphorylase and RNase PH, leads to marked growth and ribosome assembly defects. To investigate the basis for these defects, a screen for growth suppressors was performed. The majority of suppressor mutations were found to lie within nsrR, which encodes a nitric oxide (NO)-sensitive transcriptional repressor. Further analysis showed that the suppressors function not by inactivating nsrR but by causing overexpression of a downstream gene that encodes a hydrolytic RNase, RNase R. Additional studies revealed that overexpression of another hydrolytic RNase, RNase II, similarly suppressed the growth defects. These results suggest that the requirement for phosphorolytic RNases for robust cellular growth and efficient ribosome assembly can be bypassed by increased expression of hydrolytic RNases.

* Mailing address: Department of Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, FL 33136. Phone: (305) 243-7229. Fax: (305) 243-3955. E-mail: cjain{at}med.miami.edu

{triangledown} Published ahead of print on 17 July 2009.

Journal of Bacteriology, September 2009, p. 5622-5627, Vol. 191, No. 18
0021-9193/09/$08.00+0     doi:10.1128/JB.01716-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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