Ubiquitin-dependent c-Jun degradation in vivo is mediated by the delta domain

An investigation of the ubiquitin-dependent proteolysis system in the breakdown of c-Jun, a signal transducing transcription factor, reveals that only c-Jun is capable of being efficiently multiubiquitinated while its transforming counterpart, v-Jun, cannot be multiubiquitinated. The investigation involves use of a new in-vivo assay, which requires a molecularly-tagged ubiquitin and the proteins of c-Jun. The stability of v-Jun, as determined from mutagenesis experiments, reveals that the absence of 27 amino acids causes its stability.