FIG. 7.

Epigenetic states of the traJ gene in the Salmonella virulence plasmid. In the donor cell, DNA hemimethylation permits traJ transcription only in the plasmid molecule that carries a methyl group in the noncoding DNA strand. As a consequence, plasmid replication generates two epigenetic states in the traJ gene and permits traJ transcription in only one daughter plasmid molecule. The methylation states of the top and bottom DNA strands of a GATC site are depicted by an open square (nonmethylated) or closed square (methylated). The possibility that the active epigenetic state of traJ can be transferred to the recipient cell is at this stage hypothetical.