P element sequences can compensate for a deletion of the yellow regulatory region in Drosophila melanogaster.

The effects of interactions between P element and yellow regulatory sequences on the control of yellow expression were studied. The y mutations used in the analysis lack a segment of upstream sequence that extends from position -146 bp to -70 bp, relative to the transcription start site of the yellow gene. This sequence has been found to be necessary for the function of the yellow promoter. The insertion of one or two P element copies at position -69 bp compensates for the deletion in the regulatory region and restores yellow expression. After mobilization of the P element, new phenotypes were selected and molecularly characterized. Two regions in the 5' part of the P element, from 23 bp to 71 bp and from 82 bp to 108 bp, can each partially compensate for the yellow deletion. In addition, deletion derivatives of the P element were themselves able to activate yellow transcription. All such P elements retain at least 108 bp of sequence at the 5' end and 15-17 bp at the 3' end. Thus, the region of the P element from 23 bp to 108 bp contains cis-regulatory elements that can influence the transcription of neighboring genes.