Endonucleolytic cleavage of E. coli and pBR 322 DNAs by a placental DNA-binding protein

A 34,000 dalton DNA-binding protein (DBP) has been purified from human placenta. The purified protein possesses endonuclease activities capable of cleaving plasmid pBR 322 and chromosomal DNAs from E. coli. Maximum endonuclease activity was observed in the pH range of 6-9 and at 30 degrees C. The nuclease activity of the DBP was completely lost at 50 degrees C. Nitrocellulose filter binding assays indicate preferential binding of the DBP to ss DNA. The protein did not bind to apurinic DNA and UV-irradiated ds DNA. Consistent with the lack of binding of the DBP to apurinic DNA, this substrate was not cleaved by the DBP. However, native and UV-irradiated E. coli DNAs which showed poor binding were also cleaved by the DBP.