Abstract: Provided are compositions comprising an endonuclease and methods for purifying an endonuclease. One aspect of the invention provides a composition comprising at least 100 mg of an untagged endonuclease having an A260/A280 absorbance ratio of from about X to about 0.8, wherein X is less than 0.8. Another aspect of the invention provides a composition, generated by contacting a composition comprising at least 100 mg of an untagged endonuclease having an A260/A280 absorbance ratio of from about X to about 0.8, wherein X is less than 0.8, with an endonuclease binding molecule, wherein the endonuclease and the endonuclease binding molecule form a protein effector.

Abstract: One aspect of the invention provides a method of separating long polynucleotides from a composition. The method includes: introducing a composition including one or more long polynucleotides into a container including at least one boundary defined by a filter comprising a plurality of pores, wherein the pores have a smaller cross-sectional dimension than specified for the long polynucleotide's molecular weight; and applying elevated hydraulic pressure to the composition, thereby causing at least some of the one or more long polynucleotides to pass through the pores.