DNA LENGTH, BENDING, AND TWISTING CONSTRAINTS ON IS50 TRANSPOSITION

Transposition is a multistep process in which a transposable element D NA sequence moves from its original genetic location to a new site. Ea rly steps in this process include the formation of a transposition com plex in which the end sequences of the transposable element are brough t together in a structurally precise fashion through the action of the element-encoded transposase protein and the cleavage of the element f ree from the adjoining DNA. If transposition complex formation must pr ecede DNA cleavage (or nicking), then changing the length of the donor DNA between closely spaced ends should have dramatic effects on the f requency of the transposition. This question has been examined by stud ying the effects of altering donor DNA length on IS50 transposition. D onor DNA less than or equal to 64 bp severely impaired transposition. Donor DNA greater than or equal to 200 bp demonstrated high transposit ion frequencies with only modest length dependencies. Constructs with donor DNA lengths between 66 and 174 bp demonstrated a dramatic period ic effect on transposition (periodicity approximate to 10.5 bp).