If I have expressed a functional protein in e.coli,how the activity of the protein in bacterial cytoplasm will effect its survival?
If it is a metabolic enzyme and by chance it is involved in maintaining metabolic flux in the bacterium,how bacteria will make changes to the expression of the protein?
Is there any chance for over expression of target protein with out induction?
Hi, it really depends. In most cases with an overexpression plasmid the bacteria cease to grow soon after you start to produce your protein. For example the typical high expression plasmids using the T7, Arabinose, lac, tac etc tend to make so much of your RNA they become single product factories. If you are expressing things more slowly, it hard to say.
On the other question, it really depends upon the protein. There are some cases where in LB media using lac-based or lac regulated expression systems you will see production of your protein without induction. This is due to the presence of a lactose like molecule in the yeast extract. This can be suppressed with by adding glucose to the media. However, it is relatively rare that you accumulate large quantities of your protein without induction. In principal, you could place it behind a strong constitutive promoter like that for the GroEL/GroES operon and make a reasonable amount. However, if it is toxic or negatively impacts the cells metabolism you might not get what you want.
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