The cDNA coding for an acidic actinoporin, Sagartia rosea cytolysin I (Src 1), has been isolated, cloned into pGEM-T Easy Vector, and sequenced. The region encoding matured Src I was also cloned into prokaryotic expression vector pBV220 and expressed in Escherichia coli as a non-fusion protein in the form of inclusion body. Through washing and denaturation-renaturation step, the recombinant Src I was purified by Q Sepharose Fast Flow ion exchange chromatography and Phenyl Sepharose hydrophobic interaction chromatography. The two-step purification of Src I was effective, simple, and suitable for isolating large amount of high purity (above 95%) recombinant Src 1. (C) 2003 Elsevier Inc. All rights reserved.