The bacterial chromosome has to be condensed to fit inside the cell, forming a compact structure called the nucleoid, which is confined to a particular region of the cell without constriction by a membrane. Recently, the bacterial nucleoid has been shown to be far more structured than previously thought, with DNA present in topologically distinct loops, which are then arranged into macrodomains. Some proteins involved in structuring the E. coli chromosome are also known to have roles in regulating transcription. It is possible that chromosome structure could be affected by local gene expression.
Fluorescent reporter/operator systems (FROS) were used to study the positions of different inducible promoters, with and without induction. The FROS method was adapted to use a smaller insert, therefore causing less disruption to chromosome structure. The transcription factor MalI was developed as a novel FROS reporter. Of the five promoters studied only araFGH showed any movement upon induction, moving away from the cell pole. In cells at the point of division, induction of the araFGH promoter caused segregation of sister chromatids adjacent to araFGH. These results suggest that induction of promoters can cause a change in local chromosome structure, although this is not seen at all promoters
