Twin of I-POU: a two amino acid difference in the I-POU homeodomain distinguishes an activator from an inhibitor of transcription

Cell. 1992 Feb 7;68(3):491-505. doi: 10.1016/0092-8674(92)90186-g.


I-POU, a POU domain nuclear protein that lacks two conserved basic amino acids of the POU homeodomain is coexpressed in the developing Drosophila nervous system with a second POU domain transcription factor, Cf1-a. I-POU does not bind to DNA but forms a POU domain-mediated, high affinity heterodimer with Cf1-a, inhibiting its ability to bind and activate the dopa decarboxylase gene. The I-POU/Cf1-a dimerization interface encompasses only the N-terminal basic region and helices 1 and 2 of the POU homeodomains with precise amino acid and alpha-helical requirements. twin of I-POU, an alternatively spliced transcript of the I-POU gene, encodes a protein containing the two basic amino acid residues absent in I-POU. Twin of I-POU is incapable of dimerizing with Cf1-a, but can act as a positive transcription factor on targets distinct from those regulated by Cf1-a. These findings suggest that the I-POU genomic locus simultaneously generates both a specific activator and inhibitor of gene transcription, capable of modulating two distinct regulatory programs during neural development.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cloning, Molecular
  • DNA-Binding Proteins / genetics*
  • Drosophila / genetics*
  • Drosophila Proteins*
  • Genes, Homeobox / genetics*
  • Molecular Sequence Data
  • Nerve Tissue Proteins / genetics*
  • POU Domain Factors
  • Repressor Proteins / genetics*
  • Sequence Alignment
  • Trans-Activators / genetics*
  • Transcription Factors / genetics*
  • Transcription, Genetic / genetics


  • DNA-Binding Proteins
  • Drosophila Proteins
  • Nerve Tissue Proteins
  • POU Domain Factors
  • Repressor Proteins
  • Trans-Activators
  • Transcription Factors
  • USP protein, Drosophila
  • acj6 protein, Drosophila

Associated data

  • GENBANK/M84159
  • GENBANK/M84160
  • GENBANK/S72766
  • GENBANK/S72767
  • GENBANK/S72768
  • GENBANK/S72769
  • GENBANK/S72771
  • GENBANK/S82267
  • GENBANK/S82271
  • GENBANK/X63098