Bacterial Expression of IRS-1 containing GST-fusion Proteins

1.  Grow cells in 5ml (or more) of LB-Amp overnight for a starter culture.   2.  Grow larger culture using the overnight culture as a seeding culture.  The culture is grown in LB-Amp medium.  Aerate well with shaking at 37 C until OD at 600nm is ~0.6.   3.  Add the appropriate amount of IPTG stock solution to the culture to obtain a final IPTG concentration of ~2mM.   4. Continue shaking for several hours up to overnight.   5.  Spin down cells and resuspend pellet in 1/100 initial volume of culture into lysis buffer --  PBS-CMF, 2mM EDTA, 10mM DTT, PMSF, benzamidine and 0.5M NaCl.   6.  Cells are lysed by sonication at 4 C.   7.  Add Triton X-100 to 1% final concentration.   8.  Centrifuge at 20 - 30 K rpm in ultracentrifuge at 4 C for 30 min.   9.  Filter sample through a 0.45m pore size membrane.  Mix this filtered supernatant with glutathione Sepharose 4B which has been washed with PBS-CMF, 10mM DTT, 0.5M NaCl.    10.  Rotate the filtered supernatant/sepharose at 4 C for 30-60min.   11.  Spin, remove liquid and wash the sepharose 2x with PBS-CMF, 10mMDTT, 0.5M NaCl.   12.  Elute the fusion protein from the sepharose 3x with 10mM glutathione, 50mM Tris pH8.0, 10mM DTT, 0.5M NaCl.   13.  Dialyze fusion protein against 50mM Tris pH8.0, 10mM DTT, 0.5M NaCl