CHROMOSOMAL INACTIVATION OF BACILLUS-SUBTILIS EXFUSANTS - A PROKARYOTIC MODEL OF EPIGENETIC REGULATION

Epigenetic mechanisms are not exclusively reserved to eukaryotic organ isms. They are also observed in prokaryotes. As described first by Hot chkiss and Gabor, protoplast fusion between strains of Bacillus subtil is produces heterodiploid cells. Heterodiploidy is associated with the inactivation of one of the chromosomes. To study the physical structu re of the fusion product and the molecular mechanisms of inactivation, we constructed heterodiploid clones containing two chromosomes labele d by a Notl restriction fragment length polymorphism. In the progeny, we identified haploid recombinant clones that contain a chromosome car rying large regions of inactivated DNA. Studies of both recombinants o f the latter kind and heterodiploid cells indicated that chromosomal i nactivation was not determined by alteration of the inactivated nucleo tide sequence, but was probably due to a modification in the structure of the bacterial chromatin.