Nucleic Acids Research, 1987, Vol. 15, No. 20 8235-8248
© 1987
Articles |
Deletions in the tL structure upstream to the rRNA genes in the E.coli rmB operon cause transcription polarity
Max-Planck-Institut für Molekulare Genetik, Abteilung Wittmann Ihnestrasse 73, D-1000 Berlin 33, FRG
*To whom correspondence should be addressed
Received July 22, 1987. Revised September 25, 1987. Accepted September 25, 1987.
A number of deletions have been constructed within the leader region of the rrnB operon from E. coli. The deletions remove a potential transcription terminator structure downstream from an antitermination recognition sequence (Box A), which precedes the structural gone for the 16S RNA. Cells harbouring plasmids, where the terminator structure was deleted, partially or totaly, showed a reduction in growth rate under minimal growth conditions. Measurement of the ribosomal RNA synthesis rates of such cells determined by pulslabeling and hybridisation to appropriate DNA probes, showed that the amount of the more distally located 23S RNA was reduced compared to the promoter-proximal 16S RNA. This polarity in transcription, resulting in a non-stoichiometric synthesis of the ribosomal RNAs, is most likely the result of a defective antitermination. The reduction in the amount of 23S RNA in such cells is compensated for by an increase in the overall ribosomal RNA synthesis, in concordance with the ribosomal RNA feedback regulation model. The accumulation of transcripts of the tRNAGlu2 gene, coded in the spacer region between the 16S and 23S RNA genes, in cells with an altered rRNA stoichiometry supports this interpretation.