This protocol is for labeling proteins expressed from an inducible expression vector.
1. Grow cells transformed with the expression vector
in M9 minimal medium supplemented with antibiotics and 50 pg/ml of
all amino acids except methionine. Grow overnight at 37 °C.
If using 35S-EXPRESS, also omit cysteine.
2. Dilute 1:10 to 1:50 the overnight culture into fresh
M9/amino acids minus methionine medium. Shake for 2-6 hours at
37 °C until cells have entered middle log phase.
3. Induce protein expression (e.g., by adding IPTG).
4. Incubate at 37 °C for 5 minutes.
5. Add 0.2-1 mCi 35S-methionine.
6. Label for 1-10 minutes.
7. Add nonradiaoactive methionine (500 pg/ml).
8. Chill on ice.