polb cloned in pET not expressed - (Apr/08/2017 )

I have cloned a mutant human polb sequence in a pET28a vector. I have sequenced the clone, the sequence is in reading frame. When I try to expresses the protein in BL21 with IPTG, get no product. I have tried for several time, also in different concentration of IPTG, time period and temperature. Please help me.

Which fractions have you solubilised and done westerns for?

And do know this protein should express in E.coli (from literature, previous lab members, etc)?  Sometimes proteins just don't express in Ecoli.