P-Element Insertion at the polyhomeotic Gene Leads to Formation of a Novel Chimeric Protein That Negatively Regulates yellow Gene Expression in P-Element-Induced Alleles of Drosophila melanogaster

摘要

Polyhomeotic is a member of the Polycomb group ( Pc -G) of homeotic repressors. The proteins encoded by the Pc -G genes form repressive complexes on the polycomb group response element sites. The phP1 mutation was induced by insertion of a 1.2-kb P element into the 5′ transcribed nontranslated region of the proximal polyhomeotic gene. The phP1 allele confers no mutant phenotype, but represses transcription of P -element-induced alleles at the yellow locus. The phP1 allele encodes a chimeric P-PH protein, consisting of the DNA-binding domain of the P element and the PH protein lacking 12 amino-terminal amino acids. The P-PH, Polycomb (PC), and Posterior sex combs (PSC) proteins were immunohistochemically detected on polytene chromosomes in the regions of P -element insertions.