I need nuclear matrix protein fractions from an Hep G2 cell nucleus, now I have passage number 15 and I wonder if passage 20 and upper will be ok for my studies.
No Dear, it will not be ok. Better to do within 20 passage. It will be fine, if you can check the cell's DNA status by cell cycle analysis. If it is as compapre to new cells, you can proceed.
Anything is ok with these cells, provided you maintain all your experimental conditions within a range of 4-5 passages eg. p18-22/23, and constantly keep the record of the passage number for every experiment.