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Last updated date: Mar 27, 2023 Views: 293 Forks: 0
Adapted by Kevin Monahan (2017)
Original protocol by: Beijing Wu, Jason Buenrostro,
Greenleaf & Chang Lab Stanford University
November 2013
Notes/changes are bolded and underlined.
I. Cell Preparation
1. Harvest cells (no fixation), protocol to be defined by the user.
2. Spin down 50,000 cells at 500 ×g for 5 min, 4°C.
(Use very clear microcentrifuge tubes to facilitate pellet identification – DNA LoBind work well)
3. Wash once with 50 μL of cold 1x PBS buffer. Spin down at 800 ×g for 5 min, 4°C.
4. Gently pipette to resuspend the cell pellet in 50 μL of cold lysis buffer (10 mM Tris-HCl, pH 7.4, 10 mM NaCl, 3 mM MgCl2, 0.1% IGEPAL CA-630). Spin down immediately at 1000 ×g for 10 min, 4°C.
5. Discard the supernatant, and immediately continue to transposition reaction.
II. Transposition Reaction and Purification
1. Make sure the cell pellet is set on ice.
2. To make the transposition reaction mix, combine the following:
25 μL 2x TD Buffer (Illumina Cat #FC-121-1030)
2.5 μL Tn5 Transposes (Illumina Cat #FC-121-1030)
22.5 μL Nuclease Free H2O
50 μl Total
3. Gently pipette to resuspend nuclei in the transposition reaction mix.
4. Incubate the transposition reaction at 37°C for 30 min
(Test different transposition times to improve fragment size distribution) .
5. Immediately following transposition, purify using a Qiagen MinElute Kit (Zymo 5 also works).
6. Elute transposed DNA in 10 μL Elution Buffer (10mM Tris buffer, pH 8).
7. Purified DNA can be stored at -20°C.
III. PCR Amplification
1. To amplify transposed DNA fragments, combine the following in a PCR tube:
10 μL Transposed DNA
10 μL Nuclease Free H2O
2.5 μL 25μM Customized Nextera PCR Primer 1*
2.5 μL 25μM Customized Nextera PCR Primer 2* [Barcode]
25 μL NEBNext High-Fidelity 2x PCR Master Mix (New England Labs Cat #M0541)
50 μL Total
2. Cycle as follows:
(1) 72°C, 5 min
(2) 98°C, 30 sec
(3) 98°C, 10 sec
(4) 63°C, 30 sec
(5) 72°C, 1 min
(6) Repeat steps 3-5, 4x
(7) Hold at 4°C
3. In order to reduce GC and size bias in PCR, the PCR reaction is monitored using qPCR to stop amplification prior to saturation. To run a qPCR side reaction, combine the following:
5 μL 5 cycles PCR amplified DNA
4.41 μL Nuclease Free H2O
0.25 μL 25μM Customized Nextera PCR Primer 1*
0.25 μL 25μM Customized Nextera PCR Primer 2*
0.09 μL 100x SYBR Green I **
5 μL NEBNext High-Fidelity 2x PCR Master Mix
15 μL Total
* Complete list of primers available in Section VI of this protocol
**10,000x SYBR Green I is diluted in 10mM Tris buffer, pH 8 to make a 100x working solution.
4. qPCR cycle as follows: (I use white-walled PCR strips for this)
(1) 98°C, 30 sec
(2) 98°C, 10 sec
(3) 63°C, 30 sec
(4) 72°C, 1 min
(5) Repeat steps 2-4, 19x
(6) Hold at 4°C
5. The additional number of cycles needed for the remaining 45 μL PCR reaction is determined as following:
For each sample, determine maximum fluorescent intensity – then set threshold where fluorescent intensity reached 1/5th of this maximum value. Round down the CT for this threshold, this is the number of additional cycles to run (e.g. a 1/5th max CT of 5.7 = 5 more cycles)
6. Run the remaining 45 μL PCR reaction to the correct # of cycle. Cycle as follows:
(1) 98°C, 30 sec
(2) 98°C, 10 sec
(3) 63°C, 30 sec
(4) 72°C, 1 min
(5) Repeat steps 2-4, x times
(6) Hold at 4°C
7. Purify amplified library using ampure XP beads
8. QC finished library:
-run on gel/bioanalyzer to examine fragment size distribution
-run KAPA, usually 10-40nM
N.B.: This protocol is inferior to newer protocols, such OMNI-ATAC (https://doi.org/10.1038/nmeth.4396)
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