Antonie van Leeuwenhoek

, Volume 63, Issue 3, pp 323–331

The rates of macromolecular chain elongation modulate the initiation frequencies for transcription and translation inEscherichia coli


  • Michael A. Sørensen
    • Institute of MicrobiologyUniversity of Copenhagen
  • Ulla Vogel
    • Institute of Biological Chemistry BUniversity of Copenhagen
  • Kaj Frank Jensen
    • Institute of Biological Chemistry BUniversity of Copenhagen
  • Steen Pedersen
    • Institute of MicrobiologyUniversity of Copenhagen
Into The Black Box

DOI: 10.1007/BF00871227

Cite this article as:
Sørensen, M.A., Vogel, U., Jensen, K.F. et al. Antonie van Leeuwenhoek (1993) 63: 323. doi:10.1007/BF00871227


Here we show that most macromolecular biosynthesis reactions in growing bacteria are sub-saturated with substrate. The experiments should in part test predictions from a previously proposed model (Jensen & Pedersen 1990) which proposed a central role for the rates of the RNA and peptide chain elongation reactions in determining the concentration of initiation competent RNA polymerases and ribosomes and thereby the initiation frequencies for these reactions. We have shown that synthesis of ribosomal RNA and the concentration of ppGpp did not exhibit the normal inverse correlation under balanced growth conditions in batch cultures when the RNA chain elongation rate was limited by substrate supply. The RNA chain elongation rate for the polymerase transcribinglacZ mRNA was directly measured and found to be reduced by two-fold under conditions of high ppGpp levels.

In the case of translation, we have shown that the peptide elongation rate varied at different types of codons and even among codons read by the same tRNA species. The faster translated codons probably have the highest cognate tRNA concentration and the highest affinity to the tRNA. Thus, the ribosome may operate close to saturation at some codons and be unsaturated at synonymous codons. Therefore, not only translation of the codons for the seven amino acids, whose biosynthesis is regulated by attenuation, but also a substantial fraction of the other translation reactions may be unsaturated.

Recently, we have obtained results which indicate that also many ribosome binding sites are unsaturated with their substrate, i.e. with ribosomes. This observation affects the interpretation of many results obtained by use of reporter genes, because the expression from such genes is strongly influenced by the general physiology of the cell.

Key words

E. colielongation rategrowth physiologymacromolecular synthesisppGppreporter genes

Copyright information

© Kluwer Academic Publishers 1993