Ribosomes, the organelles that catalyze protein synthesis, are composed of a small subunit (40S) and a large subunit (60S) that consist of over 80 distinct ribosomal proteins. Mammalian ribosomal proteins are encoded by multigene families that contain processed pseudogenes and one functional intron-containing gene within their coding regions. Ribosomal Protein S18, also designated 40S ribosomal protein S18, RPS18, D6S218E, KE3 or HKE3, is a 152 amino acid cytoplasmic protein belonging to the ribosomal protein S13P family. A component of the 40S subunit, Ribosomal Protein S18 is a known binding partner of Cofilin and has been suggested to be a novel substrate for CaMKII. The gene encoding Ribosomal Protein S18 maps to human chromosome 6p21.32, and like most ribosomal proteins, Ribosomal Protein S18 exists as multiple processed pseudogenes that are scattered throughout the genome.