Proteolysis in plasmid DNA stable maintenance in bacterial cells

• Nucleoprotein complex processing by host proteases are important in plasmid replication and post segregational killing.
• Degradation of replication initiation proteins and antitoxin proteins of psk systems has been described for plasmids.
• The interaction of the proteases substrates with DNA can drastically change the efficiency of protein substrate degradation.
• Specific proteases themselves interact with DNA and this interaction affects their proteolytic activity.

Plasmids, as extrachromosomal genetic elements, need to work out strategies that promote independent replication and stable maintenance in host bacterial cells. Their maintenance depends on constant formation and dissociation of nucleoprotein complexes formed on plasmid DNA. Plasmid replication initiation proteins (Rep) form specific complexes on direct repeats (iterons) localized within the plasmid replication origin. Formation of these complexes along with a strict control of Rep protein cellular concentration, quaternary structure, and activity, is essential for plasmid maintenance. Another important mechanism for maintenance of low-copy-number plasmids are the toxin-antitoxin (TA) post-segregational killing (psk) systems, which prevent plasmid loss from the bacterial cell population. In this mini review we discuss the importance of nucleoprotein complex processing by energy-dependent host proteases in plasmid DNA replication and plasmid type II toxin-antitoxin psk systems, and draw attention to the elusive role of DNA in this process.