Construction and analysis of mouse strains lacking the ubiquitin ligase UBR1 (E3alpha) of the N-end rule pathway.
The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. In the yeast Saccharomyces cerevisiae, the UBR1-encoded ubiquitin ligase (E3) of the N-end rule pathway mediates the targeting of substrate proteins in part through binding to their destabilizing N-terminal residues. The functions of the yeast N-end rule pathway include fidelity of chromosome segregation and the regulation of peptide import. Our previous work described the cloning of cDNA and a gene encoding the 200-kDa mouse UBR1 (E3alpha). Here we show that mouse UBR1, in the presence of a cognate mouse ubiquitin-conjugating (E2) enzyme, can rescue the N-end rule pathway in ubr1Delta S. cerevisiae. We also constructed UBR1(-/-) mouse strains that lacked the UBR1 protein. UBR1(-/-) mice were viable and fertile but weighed significantly less than congenic +/+ mice. The decreased mass of UBR1(-/-) mice stemmed at least in part from smaller amounts of the skeletal muscle and adipose tissues. The skeletal muscle of UBR1(-/-) mice apparently lacked the N-end rule pathway and exhibited abnormal regulation of fatty acid synthase upon starvation. By contrast, and despite the absence of the UBR1 protein, UBR1(-/-) fibroblasts contained the N-end rule pathway. Thus, UBR1(-/-) mice are mosaics in regard to the activity of this pathway, owing to differential expression of proteins that can substitute for the ubiquitin ligase UBR1 (E3alpha). We consider these UBR1-like proteins and discuss the functions of the mammalian N-end rule pathway.
Kwon
Y T
YT
Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
Xia
Z
Z
Davydov
I V
IV
Lecker
S H
SH
Varshavsky
A
A
D000273:Adipose Tissue / Q000737:chemistry / Q000378:metabolism; D000581:Amidohydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000235:genetics; D002478:Cells, Cultured; D003433:Crosses, Genetic; D005227:Fatty Acids / Q000096:biosynthesis; D005347:Fibroblasts / Q000378:metabolism; D008025:Ligases / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D010641:Phenotype; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013217:Starvation / Q000378:metabolism; D014162:Transfection; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases
D005227:Fatty Acids; D011506:Proteins; D012333:RNA, Messenger; D044763:Ubiquitin-Conjugating Enzymes; C113474:UBR1 protein, human; D044767:Ubiquitin-Protein Ligases; D000581:Amidohydrolases; C425491:N-terminal asparagine amidohydrolase; D008025:Ligases