When I run my uninduced and induced crude extracts on SDS-PAGE side by side, I don see an induced band. Why?
There are a couple of possible explanations. Inserts cloned in a pMAL-p2 vector have about a 4- to 8-fold reduced level of expression when compared to the same insert in a pMAL-c2 vector. This often reduces the amount of expression to the point where there is no visible induced band. In addition, some foreign genes are poorly expressed in E. coli, even when fused to a highly expressed carrier gene. Possible explanations are message instability or problems with translation – sometimes it is due to the presence of multiple rare codons in the gene of interest, and in these cases overexpression of the corresponding tRNA can help (Schenk et al., 1995, BioTechniques 19, 196-200). Even in cases where a band is not visible, one can get yields up to 5 or 6 mg/liter of culture.
