PROTECTED P-ELEMENT TERMINI SUGGEST A ROLE FOR INVERTED-REPEAT-BINDING PROTEIN IN TRANSPOSASE-INDUCED GAP REPAIR IN DROSOPHILA-MELANOGASTER

P-element transposition is thought to occur by a cut-and-paste mechani sm that generates a double-strand break at the donor site, the repair of which can lead to internally deleted elements. We have generated a series of both phenotypically stronger and weaker allelic derivatives of vg(21), a vestigial mutant caused by a P-element insertion in the 5 ' region of the gene. Virtually all of the new alleles arose by intern al deletion of the parental element in vg(21), and we have characteriz ed a number of these internally deleted P elements. Depending upon the selection scheme used, we see a very different spectrum of amount and source of P-element sequences in the resultant derivatives. Strikingl y, most of the breakpoints occur within the inverted-repeats such that the last 15-17 bp of the termini are retained. This sequence:is known to bind the inverted-repeat-binding protein (IRBP). We propose that t he IRBP may act to preserve the P-element ends when transposition prod uces a double-strand gap. This allows the terminus to serve as a templ ate upon which DNA synthesis can act to repair the gap. Filler sequenc es found at the breakpoints of the internally deleted P elements resem ble short stretches, often in tandem arrays, of these terminal sequenc es. The structure of the filler sequences suggests replication slippag e may occur during the process of gap repair.