Phosphorylation, expression and function of the Ultrabithorax protein family in Drosophila melanogaster

Elizabeth R. Gavis, David S. Hogness

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Alternative splicing of the Ultrabithorax homeotic gene transcript generates a family of five proteins (UBX isoforms) that function as transcription factors. All isoforms contain a homeodomain within a common 99 aa C-terminal region (C-constant region) which is joined to a common 247 aa N-terminal (N-constant) region by different combinations of three small optional elements. Unlike the UBX proteins expressed in E. coli, UBX isoforms expressed in D. melanogaster cells are phosphorylated on serine and threonine residues, located primarily within a 53 aa region near the middle of the N-constant region, to form at least five phosphorylated states per isoform. Similar, if not identical states can be generated in vitro from purified E. coli UBX protein by a kinase activity in nuclear extracts from D. melanogaster cells. Temporal developmental profiles of UBX isoforms parallel those for the respective mRNAs, and all isoforms are similarly phosphorylated throughout embryogenesis. Analysis by cotransfection assays of the promoter activation and repression functions of mutant UBX proteins with various deletions in the N-constant region shows that repression is generally insensitive to deletion and, hence, presumably to phosphorylation. By contrast, the activation function is differentially sensitive to the different deletions in a manner indicating the absence of a discrete activating domain and instead, the presence of multiple activating sequences spread throughout the region.

Original languageEnglish (US)
Pages (from-to)1077-1093
Number of pages17
Issue number4
StatePublished - Aug 1991
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Developmental Biology


  • Alternative splicing
  • Bithorax complex
  • Homeotic genes
  • Protein isoforms


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