SDS-PAGE Analysis
Reagents Required
Recipes are provided in Appendix 3, page 31.
6X SDS Loading Buffer
1. Remove 10 μl of each supernatant from Step 14 (above)
to fresh tubes.
2. To these aliquots, and to the 10 μl samples retained
following steps 7 and 9 (above), add 2 μl of 6X SDS
Loading Buffer.
3. Vortex briefly and heat for 5 minutes at 90-100°C.
4. Load the samples onto a 10-12.5% SDS-polyacrylamide gel.
5. Run the gel for the appropriate length of time and stain
with Coomassie Blue to visualize the parental GST (made
in control cells carrying the parental pGEX vector) and
the fusion protein.
– Note: Transformants expressing the desired fusion protein
will be identified by the absence from total cellular
proteins of the parental 29 kDa GST and by the presence
of a novel, larger fusion protein. Parental pGEX
vectors produce a 29 kDa GST fusion protein containing
amino acids coded for by the pGEX MCS.
If the above analysis indicates that the fusion protein has
adsorbed to the Glutathione Sepharose 4B, proceed to largescale
purification as described in Procedure 11. If, on the
other hand, the fusion protein is absent from the purified
material, it may be insoluble or expressed at very low levels;
refer to the Troubleshooting Guide (page 24) for a discussion
of this problem. Interpretation is sometimes complicated
when fusion proteins break down and release the 26 kDa
GST moiety. Such cases are usually recognized by the reduced
level of the 26 kDa species, and by the series of larger, partial
proteolytic fragments above it.