SDS-PAGE problem - no bands around 20KDa (Nov/24/2008 )

hello.
I have running SDS-PAGE to detect the protein expressing in E.coli BL21.
the bands around 20KDa seemed to have disappeared, but other bands are normal.
the protein size I expecting was 22 kda, so I am not sure wether the protein have been induced.
can anyone help me ?

can you show us a picture of the gel? that would help us to diagnose your problem.

also, give more details of the gel.

12% SDS-PAGE seperating gel

it looks like a secondary buffer front. this can be caused by some component in the buffer that the sample is in (prior to adding loading buffer) or to a component in the electrode buffer (old sds can cause some problems).

if it is the sample's buffer then you can try reducing the volume of your sample (yes, the loading will be less, as well, unless you concentrate your sample) or exchanging the buffer with something similar to the loading buffer (tris pH 6.8, no sds or reducing agent).

if it is the electrode buffer then you should replace it but use different, fresher, components.