Dear Cori, yes, this is fairly common. Your setup should produce detectable expression (at least some fusion protein). I’d repeat from scratch using a fresh single colony and follow the protocol exactly. Tiny deviations often cause the “appears/disappears” effect; antibiotic throughout, induction OD, temperature, buffer composition, ....

Good luck,

From what I understand you have no way to detect your protein of interest, and what You see was only a brighter band in a coomasie stain compared to uninduced control. But half the size of the spected protein. This could be a heat-shock protein.

Are you sure the gene is cloned in the correct reading frame?

It is necessary to get access to ELISA or WB for your histag protein. This is a common technique look around your university for help.

I agree with Jahaziel, if you don't have access to westernblot, it would be difficult to confirm the presence of your protein. Without an apparatus, you can try a simple dotblot, where you put a drop of a lysate of a negative and positive colony and use anti-Histag antibody. Even with low protein expression (without a dominant band on Coomassie), you can have a satisfactory yield, but you have to confirm your protein with an antibody (anti-Histag, anti-protein, Ni-NTA conjugates) or using mass spectrometry.

But first of all, double check the DNA sequence of your construct in transformed colonies (colony PCR or regular PCR with "unpaired" primers - Forward to insert, Reverse to vector or vice-versa; then Sanger sequencing - START, STOP, reading frame, the presence of restriction sites if you use restrictases).

Btw, what do you load on PAGE? Just centifuged cells, or supernatant? The protein can be also excreted into medium if it has a signal sequence.