Ribosomal RNA operon anti-termination. Function of leader and spacer region box B-box A sequences and their conservation in diverse micro-organisms

J Mol Biol. 1989 Oct 5;209(3):345-58. doi: 10.1016/0022-2836(89)90002-8.


All Escherichia coli rrn operons show a common motif in which anti-terminator box B-box A sequences occur twice, first in the leader and again in the 16 S-23 S spacer. In this study we have analyzed several aspects of rrn anti-termination by leader and spacer anti-terminator sequences. Using DNA synthesis and a plasmid test system, we incorporated random changes into the leader anti-terminator region and examined these mutations for their ability to read through a strong terminator. We also examined anti-termination by synthetic box A and by rrn spacer region sequences. Information derived from these experiments was used to search the rrn sequences of other micro-organisms for possible anti-termination features. Our principal conclusions were that: (1) box A was sufficient for terminator readthrough; (2) we could show no positive requirement for box B in our test system; (3) many of the negative anti-terminator mutations caused a promoter up-effect in the absence of a terminator; (4) the search of rrn operons from other micro-organisms revealed that anti-terminator-like box B-box A sequences exist in leader and spacer regions of both eubacteria and archaebacteria. The frequent occurrence of this pattern suggested that the E. coli rrn anti-termination motif is widespread in nature and has been conserved in microbial evolution.

MeSH terms

  • Base Sequence
  • Cloning, Molecular
  • DNA, Bacterial / genetics
  • DNA, Ribosomal / genetics
  • Escherichia coli
  • Genes, Regulator*
  • Molecular Sequence Data
  • Mutation
  • Operon*
  • RNA, Bacterial / genetics
  • RNA, Ribosomal / genetics*
  • Restriction Mapping
  • Terminator Regions, Genetic*


  • DNA, Bacterial
  • DNA, Ribosomal
  • RNA, Bacterial
  • RNA, Ribosomal