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REACTIVITY SENSITIVITY MW (kDa)
H M R Dm Sc Endogenous
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Immunoprecipitation of Jurkat cell extracts treated with Calyculin A #9902, using Rabbit (DA1E) mAb IgG XP® Isotype Control (Magnetic Bead Conjugate) #8726 (lane 2) or Phospho-Threonine Antibody (P-Thr-Polyclonal) (Magnetic Bead Conjugate) (lane 3). Lane 1 is 10% input. The western blot was probed using Phospho-Threonine Antibody (P-Thr-Polyclonal) (HRP Conjugate) #6949.

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Immunoprecipitation for Analysis by Western Blotting

This protocol is intended for immunoprecipitation of native proteins for analysis by western immunoblot or kinase activity.

A. Solutions and Reagents

NOTE: Prepare solutions with reverse osmosis deionized (RODI) or equivalently purified water.

  1. 20X Phosphate Buffered Saline (PBS): (#9808).
  2. 10X Cell Lysis Buffer: (#9803) 20 mM Tris (pH 7.5), 150 mM NaCl, 1 mM EDTA, 1 mM EGTA, 1% Triton X-100, 2.5 mM Sodium pyrophosphate, 1 mM β-glycerophosphate, 1 mM Na3VO4, 1 μg/ml Leupeptin

    NOTE: CST recommends adding 1 mM PMSF (#8553) before use*.

  1. 3X SDS Sample Buffer: (#7722) 187.5 mM Tris-HCl (pH 6.8 at 25°C), 6% w/v SDS, 30% glycerol, 150 mM DTT, 0.03% w/v bromophenol blue
  2. 6-Tube Magnetic Separation Rack: (#7017).
  3. 10X Kinase Buffer (for kinase assays): (#9802) To Prepare 1 ml of 1X kinase buffer, add 100 µl 10X kinase buffer to 900 µl dH2O, mix.
  4. ATP (10 mM) (for kinase assays): (#9804) To prepare 0.5 ml of ATP (200 µM), add 10 µl ATP (10 mM) to 490 µl 1X kinase buffer.

B. Preparing Cell Lysates

  1. Aspirate media. Treat cells by adding fresh media containing regulator for desired time.
  2. To harvest cells under nondenaturing conditions, remove media and rinse cells once with ice-cold PBS.
  3. Remove PBS and add 0.5 ml 1X ice-cold cell lysis buffer to each plate (10 cm) and incubate the plates on ice for 5 minutes.
  4. Scrape cells off the plates and transfer to microcentrifuge tubes. Keep on ice.
  5. Sonicate samples on ice three times for 5 seconds each.
  6. Microcentrifuge for 10 minutes at 4°C, 14,000 x g, and transfer the supernatant to a new tube. If necessary, lysate can be stored at –80°C.

C. Immunoprecipitation

  1. Take 200 μl cell lysate and add 20 µl of the immobilized antibody, incubate with rotation overnight at 4°C.
  2. Microcentrifuge for 30 seconds at 4°C. Wash pellet five times with 500 µl of 1X cell lysis buffer. Keep on ice during washes.
  3. Proceed to sample analysis by western blotting or kinase activity (section D).

D. Sample Analysis

Proceed to one of the following specific set of steps.

For Analysis by Western Immunoblotting

  1. Resuspend the pellet with 20 µl 3X SDS sample buffer. Vortex, then microcentrifuge for 30 sec at 14,000 x g.
  2. Heat the sample to 95–100°C for 2-5 min and microcentrifuge for 1 min at 14,000 x g.
  3. Load the sample (15–30 µl) on a 4–20% gel for SDS-PAGE.
  4. Analyze sample by western blot (see Western Immunoblotting Protocol).

NOTE: To minimize masking caused by denatured IgG heavy chains (~50 kDa), we recommend using Mouse Anti-Rabbit IgG (Light-Chain Specific) (L57A3) mAb (#3677) or Mouse Anti-Rabbit IgG (Conformation Specific) (L27A9) mAb (#3678) (or HRP conjugate #5127). To minimize masking caused by denatured IgG light chains (~25 kDa), we recommend using Mouse Anti-Rabbit IgG (Conformation Specific) (L27A9) mAb (#3678) (or HRP conjugate #5127).

For Analysis by Kinase Assay

  1. Wash pellet twice with 500 µl 1X kinase buffer. Keep on ice.
  2. Pellet magnetic beads by placing the tubes in a magnetic separation rack (#7017) and wait 1 to 2 min for solution to clear. Wash pellet five times with 500 µl of 1X cell lysis buffer. Kepp on ice during washes.
  3. Incubate for 30 min at 30°C.
  4. Terminate reaction with 20 µl 3X SDS sample buffer. Vortex, then microcentrifuge for 30 sec.
  5. Transfer supernatant containing phosphorylated substrate to another tube.
  6. Heat the sample to 95–100°C for 2–5 min and microcentrifuge for 1 min at 14,000 x g.
  7. Load the sample (15–30 µl) on SDS-PAGE (4–20%).

posted December 2007

protocol id: 408

Product Usage Information

Application Dilutions
Immunoprecipitation 1:20

Storage: Supplied in PBS Buffer (pH 7.2), 0.1% Tween® 20. Store at 4°C. Do not aliquot the antibodies.

Specificity / Sensitivity

Phospho-Threonine Antibody (P-Thr-Polyclonal) (Magnetic Bead Conjugate) detects proteins and peptides phosphorylated at threonine residues in a manner largely independent of the surrounding amino acid sequence. The antibody is phospho-specific and may cross-react with some phospho-serine-containing sequences. By ELISA, it recognizes a wide variety of threonine-phosphorylated peptides, and by 2D gel Western blot analysis, it recognizes a large number of presumably threonine-phosphorylated proteins. Use of Phospho-Threonine-Proline Mouse mAb (P-Thr-Pro-101) #9391 is recommended to detect proteins containing threonine followed by proline.


Species Reactivity: Human, Mouse, Rat, D. melanogaster, S. cerevisiae

Source / Purification

Polyclonal antibodies are produced by immunizing animals with synthetic phospho-Thr-containing peptides. Antibodies are purified by protein A and peptide affinity chromatography.

Much of the dynamic behavior of cellular proteins, including the regulation of molecular interactions (1), subcellular localization (2), and transcriptional regulation (3) is controlled by a variety of post-translational modifications (4). Antibodies specific for these post-translational modifications are invaluable tools in the quest to understand normal and pathogenic molecular and cellular behavior.

General protein modification antibodies are designed to react with modified amino acid residues (e.g. phospho-threonine, phospho-tyrosine, acetyl-lysine, nitro-tyrosine) independently of the sequence in which they are embedded. This ability to recognize modified residues in a "context-independent" fashion gives these antibodies broad reactivities, presumably conferring upon them the ability to react with hundreds of distinct proteins. This broad pattern of reactivity makes these antibodies especially valuable in multiplex analyses and target discovery programs.


1.  Yaffe, M.B. and Elia, A.E. (2001) Curr Opin Cell Biol 13, 131-8.

2.  Appella, E. and Anderson, C.W. (2001) Eur J Biochem 268, 2764-72.

3.  Jenuwein, T. and Allis, C.D. (2001) Science 293, 1074-80.

4.  Krishna, R.G. and Wold, F. (1993) Adv Enzymol Relat Areas Mol Biol 67, 265-98.



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Use of Cell Signaling Technology (CST) Motif Antibodies within certain methods (e.g., U.S. Patents No. 7,198,896 and 7,300,753) may require a license from CST. For information regarding academic licensing terms please have your technology transfer office contact CST Legal Department at CST_ip@cellsignal.com. For information regarding commercial licensing terms please contact CST Pharma Services Department at ptmscan@cellsignal.com.