I have transduced 293T cells with GOI and empty PINCO vector that has a GFP and validated by Western blotting. However, doing a co-immunoprecipitation I'm consistently getting a signal in samples devoid of the transgene at the right MW. Note: its not a fusion protein with GFP nor light chain is not interfering as the MW is about 17kDa and exactly the same as the inputs.

Appreciate any helpful suggestion.