Ribonuclease inhibitor
![](/Images/godic/202502/07/2bnh_topview5046.png")
![Side view of porcine ribonuclease inhibitor;[1] ribbon is colored from blue (N-terminus) to red (C-terminus).](/Images/godic/202502/07/2bnh_sideview5046.png")
Ribonuclease inhibitor (RI) is a large (~450 residues, ~49 kDa), acidic (pI ~4.7), leucine-rich repeat protein that forms extremely tight complexes with certain ribonucleases. It is a major cellular protein, comprising ~0.1% of all cellular protein by weight, and appears to play an important role in regulating the lifetime of RNA.