Figure 3. Altering cohesin affects damage-induced recombination. (A) Cohesin channels recombination toward sister chromatids and away from homologous chromosomes in G_2. This model describes the role of cohesin in preventing homologous recombination (see ref. 33; the reproduction of the model was done according to the Creative Commons Attribution License -2.5 of PloS). (B) Tetraploid WT and the hypomorphic “simplex” cohesion mutant with one copy of MCD1 (for details see text and ref. 33) were irradiated with IR or UV in the G₁ or G₂ phases of the cell cycle. Presented are the frequencies of DNA damage-induced allelic recombination per unit radiation. For the x-axis, the unit dose was J/m² for UV and krad for IR. Symbols: WT G₁, white solid squares; WT G₂, white striped squares; MCD1 simplex G₁, gray solid squares; MCD1 simplex G₂, gray striped squares. (C) Four scenarios that utilize temperature changes to alter cohesin activity in the mcd1–1 temperature-sensitive mutant are presented: 23◦C, light green; 30^◦ C, red. In Scenarios 1, 2 and 4, the logarithmic growth of the culture and the G₂ arrest occur at the same temperature. In Scenario 3, the cells are grown to logarithmic phase at 30^◦ C and arrested with nocodazole for 90 min at the same temperature, but then the temperature is shifted to 23^◦ C for 30 min before irradiation while remaining in nocadazole. (D) Recombination induced by 20 krad IR or 40 J/m² for each Scenario in (C).