Mu DNA reintegration upon excision: evidence for a possible involvement of nucleoid folding.

Mutations induced by the integration of a Mugem2ts prophage can revert at frequencies around 1x10(-6). In these revertant clones, the prophage excised from its original localization is not lost but reintegrated elsewhere in the host genome. One of the most intriguing aspects of this process is that the prophage reintegration is not randomly distributed: there is a strong correlation between the original site of insertion (the donor site) and the target site of the phage DNA migration (the receptor site). In this paper, it is shown that in the excision-reintegration process mediated by Mugem2ts, the position of the initial prophage site strongly influences the location of the reintegration site. In addition, for each donor site, the receptor site is a discrete DNA region within which the excised Mu DNA can reintegrate and the two sites implicated in phage DNA migration must be located on the same DNA molecule. These data suggest the involvement of nucleoid folding in the excision-reintegration process.