Abstract
Deletion derivatives of the maize transposable element Activator (Ac) were constructed in vitro and inserted into a kanamycin resistance gene. These constructions were then introduced into tobacco protoplasts derived from plants previously transformed with Ac. The ability of each deletion derivative to excise was measured by whether or not kanamycin-resistant tobacco calli were recovered. This allowed us to determine the length of DNA present at each terminus that is required to respond to the products expressed by the Ac element present in the genome. We show that around 200 base pairs (bp) are required at both ends for excision to occur at wild-type levels. When between 100 and 200 bp were retained at one of the ends, reduced frequencies of excision were detected. With less than 100 bp remaining at either end, no excision was detected. In addition, we show that although similar lengths of DNA are required at each terminus, the termini are not interchangeable. The significance of these data is discussed with respect to the protein(s) which interact(s) with the termini of Ac.