Sindbis virus expression - cannot detect EGFP signal in hippocampal neurons (Jul/02/2007 )

I want to express my protein (A) together with EGFP, but not as fusion
proteins, since it will definitely affect the function of the protein, so I cloned
A into pIRES2-EGFP vector (I just named A-EGFP). Then clone the
whole thing into pSinRep5 vector. As control, only pIRES2-EGFP was cloned into the
pSinRep5 vector (named IRES2-EGFP).

After harvesting virus, I infected both BHK cells and hippocampal neurons at 2-3
DIV. Green fluorescence can be detected in BHK cells infected with both empty
pIRES2-EGFP and A-EGFP, although there are relatively less GFP-positive cells.
And by western blot, an increase in A protein expression level can be detected.

But in the case of hippocampal neurons, hippocampal neurons infected with IRES2-EGFP
virus showed GFP signal and the efficiency is not very high (roughly estimated to be
more than 1%, 3ul in a 6-well). But there was no GFP-positive signal in hippocampal
neurons infected with A-EGFP.

Another issue is that the sequence of my A protein contains a stop codon.

Has anyone met with this problem?