DNA binding by the KP repressor protein inhibits P-element transposase activity in vitro

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Abstract
P elements are a family of mobile DNA elements found in Drosophila . P‐element transposition is tightly regulated, and P‐element‐encoded repressor proteins are responsible for inhibiting transposition in vivo . To investigate the molecular mechanisms by which one of these repressors, the KP protein, inhibits transposition, a variety of mutant KP proteins were prepared and tested for their biochemical activities. The repressor activities of the wild‐type and mutant KP proteins were tested in vitro using several different assays for P‐element transposase activity. These studies indicate that the site‐specific DNA‐binding activity of the KP protein is essential for repressing transposase activity. The DNA‐binding domain of the KP repressor protein is also shared with the transposase protein and resides in the N‐terminal 88 amino acids. Within this region, there is a C2HC putative metal‐binding motif that is required for site‐specific DNA binding. In vitro the KP protein inhibits transposition by competing with the transposase enzyme for DNA‐binding sites near the P‐element termini.