Post translation modifications are another layer. Also, since you asked, I would like to mention protein interactions with cellular components and tissues. The

Post translation modifications are another layer. Also, since you asked, I would like to mention protein interactions with cellular components and tissues. These can be argued as just proteins interacting with each other but the extreme complexity of these higher levels and the unique phenotypes arising from them make me think they are deserved to be treated as another layer of "data decompression".