The P-Ph Protein-Mediated Repression of yellow Expression Depends on Different cis- and trans-Factors in Drosophila melanogaster

Corresponding author: Pavel Georgiev, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov St. Moscow 117334, Russia., georg{at}biogen.msk.su (E-mail)

Communicating editor: J. A. BIRCHLER

The ph^P1 allele of Drosophila melanogaster encodes a chimeric P-Ph protein that contains the DNA-binding domain of the P-element transposase and the Ph protein lacking 12 amino-terminal amino acids. It has been shown that the P-Ph protein is responsible for the formation of a repressive complex on P elements inserted at the yellow locus. Here we demonstrate that an enhancer element can suppress the P-Ph-mediated inhibition of yellow transcription. However, an increase of P-element copy number at the yellow locus overcomes the enhancer effect. The mobilization of P-element transposition induced the appearance with a high frequency of Su(y) mutations that partially or completely suppressed the inhibitory effect of ph^P1 on yellow expression. The Su(y) mutations were localized at different sites on chromosomes. One strong Su(y) mutation, sn^eP1, was found to be induced by a 1.2-kb P-element insertion into the transcribed noncoding region of the singed locus. The Su(y) mutations resulted in a high level of transcription of the 1.2-kb P element that contained the sequences encoding one DNA-binding and two protein-protein interaction domains of the transposase. The effect of Su(y) mutations can be explained by the competition between the truncated transposase encoded by a 1.2-kb P element and the P-Ph protein for binding sites on P-element insertions.