title: The Drosophila pho-like gene encodes a YY1-related DNA binding protein that is redundant with pleiohomeotic in homeotic gene silencing.
abstract: Polycomb group proteins (PcG) repress homeotic genes in cells where these genes must remain inactive during Drosophila and vertebrate development. This repression depends on cis-acting silencer sequences, called Polycomb group response elements (PREs). Pleiohomeotic (Pho), the only known sequence-specific DNA-binding PcG protein, binds to PREs but pho mutants show only mild phenotypes compared with other PcG mutants. We characterize pho-like, a gene encoding a protein with high similarity to Pho. Pho-like binds to Pho-binding sites in vitro and pho-like, pho double mutants show more severe misexpression of homeotic genes than do the single mutants. These results suggest that Pho and Pho-like act redundantly to repress homeotic genes. We examined the distribution of five PcG proteins on polytene chromosomes from pho-like, pho double mutants. Pc, Psc, Scm, E(z) and Ph remain bound to polytene chromosomes at most sites in the absence of Pho and Pho-like. At a few chromosomal locations, however, some of the PcG proteins are no longer present in the absence of Pho and Pho-like, suggesting that Pho-like and Pho may anchor PcG protein complexes to only a subset of PREs. Alternatively, Pho-like and Pho may not participate in the anchoring of PcG complexes, but may be necessary for transcriptional repression mediated through PREs. In contrast to Pho and Pho-like, removal of Trithorax-like/GAGA factor or Zeste, two other DNA-binding proteins implicated in PRE function, does not cause misexpression of homeotic genes or reporter genes in imaginal disks.
authors.affiliation: Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: J Lesley
authors.initials: JL
authors.lastname: Brown
authors.forename: Cornelia
authors.initials: C
authors.lastname: Fritsch
authors.forename: Jürg
authors.initials: J
authors.lastname: Mueller
authors.forename: Judith A
authors.initials: JA
authors.lastname: Kassis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002875:Chromosomes / Q000378:metabolism; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000502:physiology*; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000502:physiology; D004628:Embryonic Structures; D050981:Erythroid-Specific DNA-Binding Factors; D005260:Female; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D050986:YY1 Transcription Factor; D016335:Zinc Fingers
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D018398:Homeodomain Proteins; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C063460:Trl protein, Drosophila; D050986:YY1 Transcription Factor; C113295:pho protein, Drosophila; C471858:phol protein, Drosophila; C060849:z protein, Drosophila