Eukaryotic ribosomal protein S3: A constituent of translational machinery and an extraribosomal player in various cellular processes.

Ribosomal proteins from the S3 family are universal components of small ribosomal subunits in all three domains of life. In eukaryotes, ribosomal protein S3e (rpS3e) is one of 33 proteins of small subunit of the ribosome. It functions not only within the ribosome participating in translation but also as an extraribosomal player involved in a number of vitally important cellular events. RpS3e is directly implicated in translation initiation via participation in rearrangements of the small subunit structure occurring upon the binding of initiation factors eIF1 and eIF1A, which opens the ribosomal mRNA binding channel for incoming mRNA and allows scanning. Being located at the mRNA entry site of the ribosome, rpS3e is suggested to interact with mRNA part downstream of the codon at the decoding site and it could be implicated in helicase activity of the ribosome by analogy to its bacterial counterpart rpS3p. Extraribosomal functions of rpS3e are mainly based on its ability to bind to nucleic acids, although protein-protein interactions take place too. As an independent player, rpS3e is involved in DNA repair, selective gene regulation via implication in NF-κB signaling pathway, inducing apoptosis, control of expression of the own gene at the translation level and molecular interactions affecting half-life of the protein. Involvement of rpS3e in various cellular processes is mediated by specific mechanisms utilizing post-translational modifications of the protein. Here, we present accumulated to date information and current ideas concerning functions of rpS3e as a constituent of translational machinery and of the free protein as a key player in various events of the cell life.