DNA-binding proteins of the malaria vector Anopheles stephensi: purification and characterization of an endonuclease

DNA-binding proteins present in fourth instar larvae of Anopheles stephensi were isolated by affinity chromatography on native and denatured DNA cellulose columns and analyzed by electrophoresis on polyacrylamide gels. A denatured DNA-specific protein with an approximate molecular weight of 30 kDa was the predominant DNA binding protein of larvae. This protein was purified to electrophoretic homogeneity by ammonium sulfate fractionation followed by phosphocellulose chromatography. The purified 30 kDa binding protein showed an endonucleolytic activity capable of converting pBR 322 supercoiled DNA to the circular form. Maximum endonucleolytic activity was observed in the presence of 5 mM Mg(2+) at pH 7.4. Enzyme activity was completely inhibited by EDTA.