Folded chromosome in Bacillus subtilis after rifamycin treatment.

Bacterial DNA is organized as a compact nucleoid whose structure is maintained by membrane--DNA, protein--DNA and RNA--DNA interactions. We investigated the effect of the transcription inhibitor rifamycin on the structure of the nucleoid in B. subtilis. Decrease of nucleoid compactness and loss of DNA superhelicity were correlated with DNA transcription arrest, both in the wild-type and in a rifamycin-resistant strain. Moreover, the phospholipid content of the nucleoid does not change upon rifamycin treatment.