Development of nonradioactive microtiter plate assays for nuclease activity.

We have developed two microtiter plate assays for the detection of DNA cleavage by nucleases, using 3'-biotinylated oligonucleotide substrates. In the covalently linked oligonucleotide nuclease assay (CLONA), the biotinylated substrates are phosphorylated at the 5' end to facilitate their covalent immobilization on CovaLink NH plates. The cleavage of the covalently immobilized substrate by nucleases results in biotin release. The uncleaved substrate molecules are detected with an enzyme-avidin conjugate. The affinity-linked oligonucleotide nuclease assay (ALONA) makes use of substrates with a digoxigenin on the 5' end of the 3'-biotinylated DNA strand. The substrate binds specifically to the wells of streptavidin-coated microtiter plates, in which the nuclease reaction takes place. Uncleaved substrate retains the digoxigenin label, which is detected with an enzyme-labeled anti-digoxigenin antibody. We assessed the efficiency of these two assays by measuring S1 nuclease and DNase I activities, and the inhibitory effect of EDTA and aurintricarboxylic acid on the reaction. Both methods are more convenient than the standard radioactive nuclease assay and are suitable for high-throughput screening of potential nuclease inhibitors, nucleases, and catalytic antibodies. The ALONA assay was found to be more sensitive than the CLONA assay, with a performance similar to that of the standard nuclease assay.