Caffeine enhancement of digestion of DNA by nuclease S 1

Abstract

The activity of Aspergillus orzae nuclease S 1 on DNA has been investigated under varying pH and metal ion conditions. Nuclease S 1 was found to preferentially digest denatured DNA. With native DNA as substrate the enzyme could only digest the DNa when caffeine was added to the reaction mixture. The enzyme was more active in sodium acetate buffer (pH 4.5), than in either standard saline citrate (pH 7.0) or sodium phosphate buffer (pH 6.8). Caffeine was also found to affect the thermal stability of DNA, resulting in a melting profile characterized by two transitions. The first transition (poorly defined) was below the normal melting temperature of the DNA, while the next transition was at the normal melting temperature of the DNA. The susceptibity of caffeine-treated DNA to nuclease digestion seems to be a result of the local unwinding that caffeine causes in the regions of DNA that melt in the first transition. This selective destabilization presumably sensitizes the unwound regions to nuclease hydrolysis. The hydrolysates of the DNA digested by nuclease S 1 were subjected first to ion exchange chromatography followed by paper chromatography. The results from this partial characterization of the digestion products showed that they contain mononucleotides as well as oligonucleotides of varying lengths. The base composition of the mononucleotide digests suggests that caffeine has greater preference for interacting with AT base-pairs in DNA.