An unusual suicidal interaction inEscherichia coli involving nucleoid protein H-NS

Host Factor Titration by Chromosomal R-loops as a Mechanism for Runaway Plasmid Replication in Transcription Termination-defective Mutants of Escherichia coli

“…23 The mutation was further characterized in this study, and shown to be in nusG, situated 4 kb away from rpoB. Thus, the mutation was complemented by plasmid pHYD547 and its subcloned derivative pHYD549; the latter carries a 0.95 kb fragment with all of nusG and the 3 0 end of the secE gene (which is situated upstream of nusG in a bicistronic operon).…”

“…Greatly increased copy numbers of plasmids pACYC184 and pUC4K associated with lethality in nusG and rho mutants Jayashree & Gowrishankar 23 have reported that when the p15A-derived plasmid pACYC184 is introduced into the mutant now identified as nusG-G146D, the transformants grow as transparent flattened colonies that are comprised largely of dying or inviable cells. As shown in Figure 3(A), whereas the optical absorbance of cultures of freshly constructed pACYC184 derivatives of a nusG or rho mutant increase with time, the colonyforming-unit numbers decrease more than 100-fold in the stationary phase of growth.…”

“…At present, however, our data are merely descriptive of a novel phenomenon. Although the concerned hns mutations are indistinguishable from a null allele with respect to derepression of gene expression, for example, in the proU operon, 23,37,40 the null hns allele itself did not suppress the rho or nusG mutant phenotypes. Based on the facts, therefore, that the suppression is a non-null phenotype and that it is observed in both rho and nusG strains, we suggest that the mutant H-NS proteins may exert a direct influence on the molecular complexes involved in transcription elongation and Rhodependent termination.…”

“…35, 36 Jayashree & Gowrishankar 23 had identified the hns-200 allele as a spontaneous suppressor of pACYC184-mediated lethality in the strain now shown to carry the nusG-G146D mutation. Further characterization of hns-200 in this study revealed that (i) it is a G to A transition in codon 74 of hns, predicted to cause a Glu to Lys substitution (E74K), and (ii) it suppresses pACYC184-rho lethality.…”