His tagged protein expression

[Mayank Bhalla]

Hi,

I am trying to express a 15 kDa protozoan protein as a His tag fusion in
Qiagen's pQE30 vector. My problem is that the protein is being expressed
as a trimer (possibly!?) as the over expressed protein appears to be about
45 kDa on the SDS-PAGE. This high molecular weight protein gets purified
on the Ni-NTA resin supplied by Qiagen.
Can any one offer ideas so as to why it may be happening and what can I do
to get the protein of the right size? I have confirmed the construct by
sequencing the whole of the insert and the junctions.
Any help will be greatly appreciated.
Many thanks

Mayank