The Drosophila pho-like gene encodes a YY1-related DNA binding protein that is redundant with pleiohomeotic in homeotic gene silencing.
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.
Brown
J Lesley
JL
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Fritsch
Cornelia
C
Mueller
Jürg
J
Kassis
Judith A
JA
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
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