Inhibition of proteasomal degradation by the gly-Ala repeat of Epstein-Barr virus is influenced by the length of the repeat and the strength of the degradation signal.
The Gly-Ala repeat (GAr) of the Epstein-Barr virus nuclear antigen-1 is a transferable element that inhibits in cis ubiquitin/proteasome-dependent proteolysis. We have investigated this inhibitory activity by using green fluorescent protein-based reporters that have been targeted for proteolysis by N end rule or ubiquitin-fusion degradation signals, resulting in various degrees of destabilization. Degradation of the green fluorescent protein substrates was inhibited on insertion of a 25-aa GAr, but strongly destabilized reporters were protected only partially. Protection could be enhanced by increasing the length of the repeat. However, reporters containing the Ub-R and ubiquitin-fusion degradation signals were degraded even in the presence of a 239-aa GAr. In accordance, insertion of a powerful degradation signal relieved the blockade of proteasomal degradation in Epstein-Barr virus nuclear antigen-1. Our findings suggest that the turnover of natural substrates may be finely tuned by GAr-like sequences that counteract targeting signals for proteasomal destruction.
Dantuma
N P
NP
Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden.
Heessen
S
S
Lindsten
K
K
Jellne
M
M
Masucci
M G
MG
D000409:Alanine / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D005998:Glycine / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D020449:Repetitive Sequences, Amino Acid; D014452:Ubiquitins / Q000235:genetics
D019309:Epstein-Barr Virus Nuclear Antigens; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; D014452:Ubiquitins; D049452:Green Fluorescent Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000409:Alanine; D005998:Glycine