Ribosomal proteins S2, S6, S10, S14, S15 and S25 are localized on the surface of mammalian 40 S subunits and stabilize their conformation. A study with immobilized trypsin.

Trypsin immobilized on collagen membranes has been used to digest accessible ribosomal proteins of rat liver 40 S subunits. Six proteins (S2, S6, S10, S14, S15 and S25) have been found to be highly exposed on the surface of 40 S particles. They appear to be in close physical contact and localized in the same region of the subunit, most likely protruding at its surface. Electric birefringence reveals that digestion of these proteins results in unfolding of subunits: the birefringence of 40 S particles becomes negative, like that of RNA, the relaxation time undergoes a 15-fold decrease and the mechanism of orientation is drastically modified.