Hi! I'm trying to express a human protein (GST-NTCP) in E.coli (BL21 cells). The protein is cloned in pGEX6P-1 vector and is 64KDa in size. After DNA cloning, the plasmid's sequence was correct so we proceed to regrow the bacteria in 5ml of LB/amp buffer overnight. Then, we measured the absorbance using Pierce BCA kit and ran a SDS-PAGE gel using GST as positive control. On the western blot, GST band was the right size and very bright but, the GST bands on the other clones were smaller. On the 1 min exposure I have no other consistent band and on the 2-3 min exposure I have a lot of background. (See attached pictures)

How can I overcome this problem. I don't even know what I'm doing wrong. Thanks so much! :)

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