Timely resolution of sister chromatid cohesion in G2/M is essential for genome integrity. Resolution at telomeres requires the poly (ADP-ribose) polymerase tankyrase 1, but the mechanism that times its action is unknown. Here, we show that tankyrase 1 activity at telomeres is controlled by a ubiquitination/deubiquitination cycle depending on opposing ubiquitin ligase and deubiquitinase activities. In late S/G2 phase, the DNA damage-responsive E3 ligase RNF8 conjugates K63-linked ubiquitin chains to tankyrase 1, while in G1 phase such ubiquitin chains are removed by BRISC, an ABRO1/BRCC36-containing deubiquitinase complex. We show that K63-linked ubiquitin chains accumulate on tankyrase 1 in late S/G2 to promote its stabilization, association with telomeres, and resolution of cohesion. Timing of this posttranslational modification coincides with the ATM-mediated DNA damage response that occurs on functional telomeres following replication in G2. Removal of ubiquitin chains is controlled by ABRO1/BRCC36 and occurs as cells exit mitosis and enter G1, ensuring that telomere cohesion is not resolved prematurely in S phase. Our studies suggest that a cell cycle-regulated posttranslational mechanism couples resolution of telomere cohesion with completion of telomere replication to ensure genome integrity.

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In this work, numerical computations are performed to analyze the mixing characteristics and pressure drop in a spiral micromixer. The effects of variation in width and depth of the micromixer are investigated for Reynolds number ( Re) in the range of 0.1 ≤  Re≤100. Results are enumerated in terms of mass contours, streamlines, mixing index and pressure drop. It is observed that the designed spiral micromixer provides a better mixing for both low and high Re values, and moreover, the mixing index remains almost the same with the variation of the depth and width of the mixer for Re > 50. The mixing index first decreases with Re, reaches a minimum value, and thereafter again increases with a further increase in Re in the range of 0.1 ≤  Re≤50. For intermediate Reynolds number, a high mixing index is observed in micromixer having higher depth and lower width. Although the driving pressure force increases with the increase in Reynolds number, it decreases with the increase in width and depth of the micromixer.

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