The reason bacteria may end up rid of their plasmid is due to the metabolic stress the plasmid imposes on the cell, this may result in a slowed growth of the cell, thus plasmid free segregants outgrow plasmid bearing segregants.
The cell overcomes this problem through use of 'post segregational killing systems':

ColE1 containing cells secrete colicin, cells that do not contain the ColE1 plasmid do not have the imm gene and thus do not produce the immunity protein and die.
F encodes 2 host killing 'toxin/antitoxin' systems: hok/sok and ccdA/ccdB (ccdA is a stable protein that inhibits DNA gyrase, whereas ccdB is unstable inhibitor of ccdA)

hok/sok killing mechanism operates much the same as ccdA/B but operates on the RNA level. Hok is a host killing peptide, translated from a stable (20min half life) mRNA. Sok is an unstable (5 min half life) antisense that binds to Hok mRNA and prevents it being translated.

	Creado por Austin Davies hace alrededor de 8 años

Accessory genome lecture block