S-protein-2xFLAG-Streptavidin binding peptide (SFB)-tagged TLK1 or SFB-TLK2 were transfected into 4x 15 cm plates of HEK293T cells. Cells were harvested 24 hours after transfection using NETN buffer (150 mM NaCl, 0.5 mM EDTA, 20 mM Tris-HCl pH 8.0, 0.5% NP-40) supplemented with 2 µg/mL aprotinin (Thermo, AAJ60237MB) and 5 µg/mL pepstatin A (Thermo, PI78432) at 4ºC for 20 minutes. Lysates were centrifuged at 9,000 x g, 4ºC for 20 minutes to yield supernatant as soluble fraction. Soluble fractions were incubated with streptavidin sepharose (200 µl) (GE Healthcare, GE17-5113-01) at 4ºC for 1 hour followed by washing with NETN buffer three times. The protein complexes were eluted with 2 mg/mL biotin at 4ºC for 1 hour. The eluents were then incubated with S-protein agarose (EMD Millipore, 69704-3) overnight at 4ºC, washed three times with NETN buffer, and eluted in 1x Laemmli buffer.