JM109 has LacZΔM15 in a F' episome (lac operon in the chromosome was deleted).
So, JM109 can be used in a-complementation test. Then, how is it possible that JM109 grows with lactose? (LacZΔM15 doesn't have B-galactosidase activity.)
Dear Yong-Wook Chin, I agree with Micheal's statement - the strain should not grow on lactose as the sole carbon source. If it does, then it is likely that your strain has been mixed up with another. You could confirm this by checking aspects of the JM109 genotype (F´ traD36 proA+B+ lacIq Δ(lacZ)M15/ Δ(lac-proAB) glnV44 e14- gyrA96 recA1 relA1 endA1 thi hsdR17), but I would suggest that it would be easier and less worrying if you buy a sample of JM109 from Promega and use that instead. Regards, Andrew.
Many thanks for reply.
I agree with the statement - JM109 cannot grow on lactose as sole carbon source.
Actually, the strain is JM109(DE3).
I saw information about the strain: "JM109(DE3) cannot be used for blue/white selection." Maybe it menas JM109(DE3) has B-galactosidase activity and can grow with lactose. Then, how is it possible?
I'm not completely certain of why you can't use JM109(DE3) for blue white screening, but I would guess the reason is that you would need to add IPTG in order for blue white screening to work, but that would induce expression of the T7 polymerase so may be toxic to the cell.
I got the answer for my question.
The bacteriophage DE3 encodes the lacI gene and the beginning of the lacZ gene. This portion of the lacZ gene encodes the alpha peptide of beta-galactosidase. Thus DE3 strains will express both the alpha and omega fragments of beta-gal and will form a functional beta-gal protein.
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