Strand transfer reactions were initiated by addition of the target DNA to preformed , Tn5 paired end complexes ( analogous to synaptic complexes ) containing two protomers of Tnp and two end sequence containing 40 - mer DNAs . The 5 0 -end of the NTS contained either a hydroxyl or a phosphate as indicated . The reactions were performed in the presence of Mg 2 + and were terminated at the indicated times . Strand transfer products were visualized through agarose gel electrophoresis . Two types of products are observed in this reaction : single end strand transfer events , in which one labeled 40 - mer DNA is covalently linked to the one strand of pUC19 DNA ( migrating as a relaxed circle ) , and double end strand transfer events in which a linear form of the target is generated ( Figure 2 ) . In our experiments the double end strand transfer products formed in the strand transfer assays with the 5 0 phosphate substrate are detected 5 min after the target DNA and Mg 2 + have been added . In contrast , double end strand transfer products formed with the 5 0 -hydroxyl substrate were evident no earlier than after 1 h incubation . The results of these assays demonstrated that , in the presence of the phosphate group on the NTS 5 0 -end , the completion of the transposition process ( characterized by the double end strand transfer band ) occurs $ 30 times faster compared to the data for 5 0 hydroxyl DNA ( Figure 2B ) . Qualitatively similar results are obtained by summing the single end transfer and double end transfer products . This finding clearly indicates that the 5 0 phosphate on the NTS plays an important role in the target capture and/or the DNA strand transfer reaction ( because we measure these two events through a strand transfer assay , we will use ' strand transfer ' to refer to the combination of both events ) .