Hello Kevin, I never did sonication of 293T cells but in case I am starting with new cells I am doing several different times of sonication as a test run first before doing the actual experiment. After checking the chromatin size on an agarose gel in comparison to before sonication I choose which way I will sonicate my sample. In case you are going to use a Biorupter I would try try first the following: on max. power 3 times 7 sec with changing the ice/water bath in between, 5 times 7 sec versus 8 times 7 sec. The liquid should be 300-400 µL in each tube. In case you are using these one needle things (no idea how they are called), try first: 6, 10 and 14 times 15 sec with 20% vs. 40%. With those machines you need to test more because it might be an older machine where you need higher amplitude or a newer one with lower amplitude (not getting to warm). Use a glas beaker with ethanol/water/ice bath below your sample of max 1 mL in 15 mL tube. I hope that will give you a kind of an idea. Good luck!

Hi Nicole, thanks for the advice, this will be very helpful. What kind of cell concentrations have worked well for you in the past?

Hi Kevin, I tried to be at roughly 1 times 10exp7 cells per mL.

Thanks again, Nicole. It looks like I'm on the right track and just need to optimize the socination step.

That sounds good. Good luck! Use the sonication conditions which are giving you mostly fragments of smaller than 3,000 bp but are not so strong that you are destroying everything. ;-) Good luck!