title: Gly-Ala repeats induce position- and substrate-specific regulation of 26 S proteasome-dependent partial processing.
abstract: Partial degradation or regulated ubiquitin proteasome-dependent processing by the 26 S proteasome has been demonstrated, but the underlying molecular mechanisms and the prevalence of this phenomenon remain obscure. Here we show that the Gly-Ala repeat (GAr) sequence of EBNA1 affects processing of substrates via the ubiquitin-dependent degradation pathway in a substrate- and position-specific fashion. GAr-mediated increase in stability of proteins targeted for degradation via the 26 S proteasome was associated with a fraction of the substrates being partially processed and the release of the free GAr. The GAr did not cause a problem for the proteolytic activity of the proteasome, and its fusion to the N terminus of p53 resulted in an increase in the rate of degradation of the entire chimera. Interestingly the GAr had little effect on the stability of EBNA1 protein itself, and targeting EBNA1 for 26 S proteasome-dependent degradation led to its complete degradation. Taken together, our data suggest a model in which the GAr prevents degradation or promotes endoproteolytic processing of substrates targeted for the 26 S proteasome by interfering with the initiation step of substrate unfolding. These results will help to further understand the underlying mechanisms for partial proteasome-dependent degradation.
authors.affiliation: INSERM U716, Institut de Génétique Moléculaire, Université Paris 7, Hôpital St. Louis, 75010 Paris, France.
authors.forename: Chrysoula
authors.initials: C
authors.lastname: Daskalogianni
authors.forename: Sébastien
authors.initials: S
authors.lastname: Apcher
authors.forename: Marco M
authors.initials: MM
authors.lastname: Candeias
authors.forename: Nadia
authors.initials: N
authors.lastname: Naski
authors.forename: Fabien
authors.initials: F
authors.lastname: Calvo
authors.forename: Robin
authors.initials: R
authors.lastname: Fåhraeus