Variations in UDP-N-acetylglucosamine and UDP-N-acetylmuramyl-pentapeptide pools in Escherichia coli after inhibition of protein synthesis

Abstract

The pool levels of the nucleotide precursors of peptidoglycan were analyzed after inhibition of protein synthesis in various Escherichia coli strains. In all cases UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylmuramyl-pentapeptide (UDP-MurNAc-pentapeptide) cell pools increased upon treatment with chloramphenicol or tetracycline. Similar results were observed after the treatment of K-12 strains with valine. Since the intermediate nucleotide precursors did not accumulate after the arrest of protein synthesis and since a feedback mechanism was unlikely, the increases of the UDP-MurNAc-pentapeptide pool appeared as a consequence of that of the UDP-GlcNAc pool by the unrestricted functioning of the intermediate steps of the pathway. The highest increase (sixfold) of UDP-GlcNAc was observed with strain K-12 HfrH growing in minimal medium and treated with chloramphenicol. When a pair of isogenic Rel+ and Rel- strains were considered, both the UDP-GlcNAc and UDP-MurNAc-pentapeptide pools increased upon treatment with chloramphenicol or valine. However, the UDP-GlcNAc pool of the Rel+ strain was at a high natural level, which increased only moderately (20%) after the addition of valine. The increase of the UDP-GlcNAc pool after the various treatments could be due to an effect on some upstream step by an unknown mechanism. The possible correlations of the variations of the precursor pools with the rate of synthesis and extent of cross-linking of peptidoglycan were also considered.