An essential function of ribosomal protein S1 in messenger ribonucleic acid translation.

A gentle and efficient method for selectively removing S1 from ribosomes was developed: the S1-free translation system prepared from such ribosomes is stimulated 10-20-fold (depending on the mRNA) by a stoichiometric amount of added purified S1. With this system, we examined the activity of mono- and di-N-ethylmaleimide derivatives of S1 in protein synthesis using synthetic and natural mRNAs and electrophoretic analysis of the translation products. The results show that ribosomes containing such modified S1's are functionally active although at a somewhat lower level (50-80% activity). Since treatment of S1 with N-ethylmaleimide abolishes the helix-destabilizing ability of S1, we conclude that this ability is not primarily responsible for S1's biological function. A new model for the role of S1 is proposed on the basis of the physical, structural, and RNA-binding properties of S1.