UPL1 and 2, two 405 kDa ubiquitin-protein ligases from Arabidopsis thaliana related to the HECT-domain protein family

Plant J. 1999 Oct;20(2):183-95. doi: 10.1046/j.1365-313x.1999.00590.x.


The ubiquitin/26S proteasome pathway is a major route for degrading abnormal and important short-lived regulatory proteins in eukaryotes. Covalent attachment of ubiquitin, which triggers entry of target proteins into the pathway, is accomplished by an ATP-dependent reaction cascade involving the sequential action of three enzymes, E1s, E2s and E3s. Although much of the substrate specificity of the pathway is determined by E3s (or ubiquitin-protein ligases, UPLs), little is known about these enzymes in plants and how they choose appropriate targets for ubiquitination. Here, we describe two 405 kDa E3s (UPL1 and 2) from Arabidopsis thaliana related to the HECT-E3 family that is essential in yeast and animals. UPL1 and 2 are encoded by 13 kbp genes 26 cM apart on chromosome I, that are over 95% identical within both the introns and exons, suggesting that the two loci arose from a recent gene duplication. The C-terminal HECT domain of UPL1 is necessary and sufficient to conjugate ubiquitin in vitro in a reaction that requires the positionally conserved cysteine within the HECT domain, E1, and an E2 of the UBC8 family. Given that HECT E3s help define target specificity of the ubiquitin conjugation, a continued characterization of UPL1 and 2 should be instrumental in understanding the functions of ubiquitin-dependent protein turnover in plants and for identifying pathway substrates.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / genetics*
  • Arabidopsis Proteins*
  • Ligases / genetics*
  • Ligases / isolation & purification
  • Molecular Sequence Data
  • Peptide Hydrolases / genetics*
  • Proteasome Endopeptidase Complex*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Alignment
  • Ubiquitin-Protein Ligase Complexes*
  • Ubiquitin-Protein Ligases


  • Arabidopsis Proteins
  • Ubiquitin-Protein Ligase Complexes
  • UPL2 protein, Arabidopsis
  • Ubiquitin-Protein Ligases
  • Peptide Hydrolases
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease
  • Ligases
  • UPL1 protein, Arabidopsis

Associated data

  • GENBANK/AF127564
  • GENBANK/AF127565