Abstract
Ubiquitin E3 ligases target their substrates for ubiquitination, leading to proteasome-mediated degradation or altered biochemical properties. The ubiquitin ligase Ubr2, a recognition E3 component of the N-end rule proteolytic pathway, recognizes proteins with N-terminal destabilizing residues and plays an important role in spermatogenesis. Tex19.1 (also known as Tex19) has been previously identified as a germ cell-specific protein in mouse testis. Here we report that Tex19.1 forms a stable protein complex with Ubr2 in mouse testes. The binding of Tex19.1 to Ubr2 is independent of the second position cysteine of Tex19.1, a putative target for arginylation by the N-end rule pathway R-transferase. The Tex19.1-null mouse mutant phenocopies the Ubr2-deficient mutant in three aspects: heterogeneity of spermatogenic defects, meiotic chromosomal asynapsis, and embryonic lethality preferentially affecting females. In Ubr2-deficient germ cells, Tex19.1 is transcribed, but Tex19.1 protein is absent. Our results suggest that the binding of Ubr2 to Tex19.1 metabolically stabilizes Tex19.1 during spermatogenesis, revealing a new function for Ubr2 outside the conventional N-end rule pathway.
Highlights
The N-end rule pathway is a ubiquitin-dependent proteolytic system [1,2]
Mass spectrometry analysis identified this band as Ubr2, one of the recognition E3 components of the N-end rule pathway [13]
Co-transfection of NIH3T3 cells followed by coimmunoprecipitation and Western blot analysis further support the interaction between Tex19.1 and Ubr2 (Fig. 2A, Lane 1)
Summary
The N-end rule pathway is a ubiquitin-dependent proteolytic system [1,2]. In this pathway, the stability of proteins is defined by their N-terminal amino acids that are distinguished into stabilizing and destabilizing residues. The stability of proteins is defined by their N-terminal amino acids that are distinguished into stabilizing and destabilizing residues The latter constitute so-called Ndegrons, which are signatures for degradation of short-lived proteins. Cysteine at position 2 (after methionine) is a unique type of destabilizing residue in mammalian cells. The mammalian genome encodes at least four UBR members (Ubr, Ubr, Ubr and Ubr5) characterized by the UBR box, a ,70-residue zinc finger-like domain [2,6]
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