IDENTIFICATION AND CHARACTERIZATION OF A PRE-CLEAVAGE SYNAPTIC COMPLEX THAT IS AN EARLY INTERMEDIATE IN TN-10 TRANSPOSITION

The Tn10 transposition reaction has been reconstituted in vitro on sho rt linear substrate fragments encoding transposon ends. This permits t he direct detection of protein-DNA complexes formed during transpositi on by gel retardation analysis. We demonstrate that a stable synaptic complex containing transposase and a pair of transpsoson ends forms ra pidly and efficiently, prior and prerequisite to the double-strand cle avages involved in transposon excision. These observations extend the general analogies between the Tn10 and Mu transposition reactions, and also reveal significant differences between the two cases. The speed and simplicity of synaptic complex formation in the Tn10/IS10 reaction is suitable for a modular insertion sequence. In contrast, the relati ve slowness and complexity of this process in the Mu is necessary to p ermit transposition immunity and control of transposition by Mu repres sor protein, two features specifically important for a temperate bacte riophage. Further dissection of the reaction leads to a tentative work ing model for events preceding the first double-strand cleavage.