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Journal of Bacteriology, April 2005, p. 2758-2767, Vol. 187, No. 8
0021-9193/05/$08.00+0     doi:10.1128/JB.187.8.2758-2767.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Participation of 3'-to-5' Exoribonucleases in the Turnover of Bacillus subtilis mRNA

Irina A. Oussenko,1 Teppei Abe,2 Hiromi Ujiie,3 Akira Muto,2,3 and David H. Bechhofer1*

Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, New York University, New York, New York,1 Department of Biochemistry and Biotechnology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki,2 The United Graduate School of Agricultural Science, Iwate University, Morioka, Japan3

Received 7 December 2004/ Accepted 12 January 2005

Four 3'-to-5' exoribonucleases have been identified in Bacillus subtilis: polynucleotide phosphorylase (PNPase), RNase R, RNase PH, and YhaM. Mutant strains were constructed that were lacking PNPase and one or more of the other three ribonucleases or that had PNPase alone. Analysis of the decay of mRNA encoded by seven small, monocistronic genes showed that PNPase was the major enzyme involved in mRNA turnover. Significant levels of decay intermediates, whose 5' ends were at the transcriptional start site and whose 3' ends were at various positions in the coding sequence, were detected only when PNPase was absent. A detailed analysis of rpsO mRNA decay showed that decay intermediates accumulated as the result of a block to 3'-to-5' processivity at the base of stem-loop structures. When RNase R alone was present, it was also capable of degrading mRNA, showing the involvement of this exonuclease in mRNA turnover. The degradative activity of RNase R was impaired when RNase PH or YhaM was also present. Extrapolation from the seven genes examined suggested that a large number of mRNA fragments was present in the PNPase-deficient mutant. Maintenance of the free ribosome pool in this strain would require a high level of activity on the part of the tmRNA trans translation system. A threefold increase in the level of peptide tagging was observed in the PNPase-deficient strain, and selective pressure for increased tmRNA activity was indicated by the emergence of mutant strains with elevated tmRNA transcription.


* Corresponding author. Mailing address: Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine of New York University, New York, NY 10029. Phone: (212) 241-5628. Fax: (212) 996-7214. E-mail: david.bechhofer{at}mssm.edu.


Journal of Bacteriology, April 2005, p. 2758-2767, Vol. 187, No. 8
0021-9193/05/$08.00+0     doi:10.1128/JB.187.8.2758-2767.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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