A Drosophila protein that imparts directionality on a chromatin insulator is an enhancer of position-effect variegation

Cell. 1995 Aug 25;82(4):587-97. doi: 10.1016/0092-8674(95)90031-4.


The suppressor of Hairy wing (su(Hw)) protein inhibits the function of transcriptional enhancers located distally from the promoter with respect to the location of su(Hw)-binding sites. This polarity is due to the ability of the su(Hw)-binding region to form a chromatin insulator. Mutations in modifier of mdg4 (mod(mdg4)) enhance the effect of su(Hw) by inhibiting the function of enhancers located on both sides of the su(Hw)-binding region. This inhibition results in a variegated expression pattern, and mutations in mod(mdg4) act as classical enhancers of position-effect variegation. The mod(mdg4) and su(Hw) proteins interact with each other. The mod(mdg4) protein controls the nature of the repressive effect of su(Hw): in the absence of mod(mdg4) protein, su(Hw) exerts a bidirectional silencing effect, whereas in the presence of mod(mdg4), the silencing effect is transformed into unidirectional repression.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Animals
  • Chromatin / genetics
  • DNA-Binding Proteins / genetics
  • Drosophila Proteins*
  • Drosophila melanogaster / genetics*
  • Enhancer Elements, Genetic
  • Gene Expression Regulation
  • Genes, Insect
  • Genes, Suppressor
  • Leucine Zippers / genetics
  • Molecular Sequence Data
  • Mutation
  • Nuclear Proteins / genetics
  • Phenotype
  • Repressor Proteins / genetics*
  • Transcription Factors / genetics


  • Chromatin
  • DNA-Binding Proteins
  • Drosophila Proteins
  • Nuclear Proteins
  • Repressor Proteins
  • Transcription Factors
  • mod(mdg4) protein, Drosophila
  • su(Hw) protein, Drosophila

Associated data

  • GENBANK/U30905
  • GENBANK/U30913
  • GENBANK/U30914