는 pEGFP-C2 에 유전자를 Cloning 해서 Transfection 후에 진행 하고 있습니다
-> Do you mean that protein X is fused with GFP such as GFP-X?
If so, IP by anti-GFP results in purification of GFP-X.
The MW of purified protein should be 26 + Y. Here, Y is the MW of protein X.