40S ribosomal protein S18, also known as RPS18, belongs to the ribosomal protein S13P family. Ribosomes, the organelles that catalyze protein synthesis, consist of a small 40S subunit and a large 60S subunit. RPS18 is a known binding partner of Cofilin and has been suggested to be a novel substrate for CaMKII. Recombinant human RPS18 protein, fused to His-tag at N-terminus, was expressed in E.coli.