Green fluorescent protein was purified from sonicated recombinant Escherichia coli and its mutant obtained after exposure to UV light. The latter overexpresses green fluorescent protein. The two-step procedure consisted of a two-phase aqueous extraction with PEG/salt and precipitation of the proteins from PEG phase by free Zn2+. The recoveries of green fluorescent protein were 73 and 83% in the cases of recombinant E coli and its mutant, respectively. The corresponding fold purifications were 24 and 9, respectively. In both cases, the purified protein showed a single band on SDS-PAGE corresponding to 28 kDa. (C) 2004 Elsevier Inc. All rights reserved.