Identification of the DNA sequence required for transposition immunity of the gamma delta sequence

A plasmid containing the transposon gamma delta sequence was immune to further insertion of gamma delta (transposition immunity). Plasmids carrying a fragment containing either 0.2 kilobase pairs of the gamma end or 0.4 kilobase pairs of the delta end of the gamma delta sequence were immune, and other parts of the gamma delta sequence did not confer immunity. The terminal 38-base-pair (bp) sequence of the delta end of the gamma delta was sufficient to confer immunity, the 38-bp sequence of the gamma end conferred only moderate immunity, and the terminal 35-bp sequence, which was completely identical at both the gamma and delta ends, was insufficient to confer immunity.