Terminus DNA loss in <i>recA</i> mutants.

<p>(<u>A) Time-lapse analysis of focus loss in <i>recA</i> (left panel), <i>recA recD</i> (middle panel) and <i>recA recB</i> (right panel) mutants.</u> Time-lapse experiments were carried out on M9 glucose agarose pads at 30°C with pictures taken every 10 min. Cells contain <i>ydeV</i>::<i>parS</i>_pMT1 and express the ParB_pMT1 protein from the gene inserted into the chromosome. The numbers in the lower left corner of the pictures indicate the frame number. For reasons of space limitations some frames are skipped. Cells that generate a focus-less cell during division are circled with a full white line. Most often two foci can be seen before division, which shows that focus loss results from the degradation of a DNA sequence that has been previously replicated. Cells that have lost the focus are circled with a dashed white line. These focus-less cells generally do not divide. In the <i>recA</i> mutant example (left), focus loss is transmitted for one generation (images number 1 and 13) and then the focus-carrying cell returns to normal divisions (images 33–47). In the <i>recA recD</i> mutant transmission is increased compared to the <i>recA</i> mutant, two examples are shown. The cell on the left generates a focus-less cell at each cell division for 3 generations (transmitted event, images number 3, 15, 22) before returning to a normal division (images 27–36). The cell on the right generates a focus-less cell (image 3) and then divides normally once (images 15–18, non-heritable event). At the next generation each focus-containing cell undergoes a new initial event (image 36); these late initial events were counted but not used to quantify heredity since the following generations were not visible. In the <i>recA recB</i> example (right), a focus-less cell is generated during 5 consecutive generations. Examples of focus-less cell production from a cropped bacterium, but for which all frames taken every 10 min are shown, can be seen in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.s011" target="_blank">S1 Video</a> (<i>recB</i>), <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.s012" target="_blank">S2 Video</a> (<i>recA</i>), <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.s013" target="_blank">S3 Video</a> (<i>recA</i> elongated cells) and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.s014" target="_blank">S4 Video</a> (<i>recA recD</i>). A schematic representation showing the frequency of initial and heritable events is shown below the time-lapse images. (B) <u>MFA analysis of terminus DNA loss in the <i>recA</i> (left panel), <i>recA recD</i> (middle panel) and <i>recA recB</i> (right panel) mutant</u>s. Experiments are realized and plotted as in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.g001" target="_blank">Fig 1C</a>. Original MFA data are shown in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1007256#pgen.1007256.s006" target="_blank">S2 Fig</a>.