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Journal of Bacteriology, June 1999, p. 3803-3809, Vol. 181, No. 12
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Construction and Initial Characterization of Escherichia coli Strains with Few or No Intact Chromosomal rRNA Operons

Tsuneaki Asai,dagger Ciarán Condon,Dagger Justina Voulgaris,§ Dmitry Zaporojets, Binghua Shen, Michaal Al-Omar, Craig Squires, and Catherine L. Squires*

Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111

Received 19 January 1999/Accepted 21 April 1999

The Escherichia coli genome carries seven rRNA (rrn) operons, each containing three rRNA genes. The presence of multiple operons has been an obstacle to many studies of rRNA because the effect of mutations in one operon is diluted by the six remaining wild-type copies. To create a tool useful for manipulating rRNA, we sequentially inactivated from one to all seven of these operons with deletions spanning the 16S and 23S rRNA genes. In the final strain, carrying no intact rRNA operon on the chromosome, rRNA molecules were expressed from a multicopy plasmid containing a single rRNA operon (prrn). Characterization of these rrn deletion strains revealed that deletion of two operons was required to observe a reduction in the growth rate and rRNA/protein ratio. When the number of deletions was extended from three to six, the decrease in the growth rate was slightly more than the decrease in the rRNA/protein ratio, suggesting that ribosome efficiency was reduced. This reduction was most pronounced in the Delta 7 prrn strain, in which the growth rate, unlike the rRNA/protein ratio, was not completely restored to wild-type levels by a cloned rRNA operon. The decreases in growth rate and rRNA/protein ratio were surprisingly moderate in the rrn deletion strains; the presence of even a single operon on the chromosome was able to produce as much as 56% of wild-type levels of rRNA. We discuss possible applications of these strains in rRNA studies.

* Corresponding author. Mailing address: Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6947. Fax: (617) 636-0337. E-mail: csquires_rib{at}opal.tufts.edu.

dagger Present address: Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114.

Dagger Present address: Institut de Biologie Physico-Chimique, 75005 Paris, France.

§ Present address: Department of Biological Sciences, Columbia University, New York, NY 10027.

Journal of Bacteriology, June 1999, p. 3803-3809, Vol. 181, No. 12
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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