A novel mechanism for P element homing in Drosophila

P element insertion is essentially random at the scale of the genome. Howev er, P elements containing regulatory sequences from Drosophila engrailed an d polyhomeotic genes and from the Bithorax and Antennapedia complexes show some insertional specificity by frequently inserting near the parent gene ( homing) and/or near genes containing Polycomb group response elements (pref erential insertion). This phenomenon is thought to be mediated by Polycomb group proteins. In this report, we describe a case of homing of P elements containing regulatory sequences of the linotte gene, This homing occurs wit h high frequency (up to 20% of the lines) and high precision (inserted into a region of <1 kilobase),We present evidence showing that it is not mediat ed by Polycomb group proteins but by a new, as yet unknown, mechanism, We a lso suggest that P element homing could be a more frequent phenomenon than generally assumed and that it could become a powerful tool of Drosophila re verse genetics, for which there is no other described gene targeting techni que.