CHROMOSOMAL DOMAINS OF SUPERCOILING IN SALMONELLA-TYPHIMURIUM

The chromosomes of enteric bacteria are divided into about 50 independ ently supercoiled domains. It is not known whether the net level of DN A supercoiling is similar in each domain, or whether the domains are d ifferentially supercoiled. We have addressed this question genetically , using a supercoiling-sensitive promoter to probe the relative levels of supercoiling at defined points around the Salmonella typhimurium c hromosome. We conclude that, within the limits of resolution of this a pproach, the level of supercoiling does not differ significantly betwe en chromosomal domains, and that each domain responds in a similar fas hion to factors that perturb supercoiling. These findings have implica tions for the organization of the bacterial genome.