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Science 309 (5731): 127-130

Copyright © 2005 by the American Association for the Advancement of Science

Ubiquitination on Nonlysine Residues by a Viral E3 Ubiquitin Ligase

Ken Cadwell, and Laurent Coscoy*

Abstract: Ubiquitination controls a broad range of cellular functions. The last step of the ubiquitination pathway is regulated by enzyme type 3 (E3) ubiquitin ligases. E3 enzymes are responsible for substrate specificity and catalyze the formation of an isopeptide bond between a lysine residue of the substrate (or the N terminus of the substrate) and ubiquitin. MIR1 and MIR2 are two E3 ubiquitin ligases encoded by Kaposi's sarcoma–associated herpesvirus that mediate the ubiquitination of major histocompatibility complex class I (MHC I) molecules and subsequent internalization. Here, we found that MIR1, but not MIR2, promoted down-regulation of MHC I molecules lacking lysine residues in their intracytoplasmic domain. In the presence of MIR1, these MHC I molecules were ubiquitinated, and their association with ubiquitin was sensitive to ß2-mercaptoethanol, unlike lysine-ubiquitin bonds. This form of ubiquitination required a cysteine residue in the intracytoplasmic tail of MHC I molecules. An MHC I molecule containing a single cysteine residue in an artificial glycine and alanine intracytoplasmic domain was endocytosed and degraded in the presence of MIR1. Thus, ubiquitination can occur on proteins lacking accessible lysines or an accessible N terminus.

Department of Molecular and Cell Biology, 142 Life Sciences Addition Room 3200, Berkeley, CA 94720, USA.

* To whom correspondence should be addressed. E-mail: lcoscoy{at}

Ubiquitination is a highly regulated process conserved in all eukaryotes (1, 2) that regulates many fundamental cellular processes. Many pathogens mimic, block, or redirect the activity of the ubiquitin system. The modulators of immune recognition (MIR) 1 and 2, two proteins encoded by Kaposi's sarcoma–associated herpesvirus (KSHV), specifically down-regulate the expression of MHC I from the surface of infected cells, presumably to prevent lysis of infected cells by cytotoxic T lymphocytes (36). MIR1 and MIR2 are highly homologous structurally and functionally, and they belong to a large family of E3 ubiquitin ligases (3, 7). E3 ubiquitin ligases function as adaptors to facilitate positioning and transfer of ubiquitin (Ub) from an E2 enzyme directly onto the E3-bound substrate (1). The nature of the bond between Ub and its substrate has been well characterized: The Ub C-terminal glycine carboxy group forms an isopeptide bond with the {epsilon}-amino group of lysine residues or, less commonly, with the amino group at the N terminus of the substrate protein (8). MIR proteins recruit E2 enzymes with their N-terminal RING-CH domain (3). Either direct or indirect interactions between the transmembranes of the MIRs and MHC I molecules ultimately lead to the ubiquitination of lysine residues present in the MHC I intracytoplasmic tail (3, 9). Ubiquitinated molecules are then endocytosed and degraded by the lysosome (3, 7, 1012). Mutating all the lysines to arginines in the intracytoplasmic domain of HLA.B7 (henceforth referred to as the HLA.B7 2R mutant or lysineless HLA.B7) abolishes internalization mediated by MIR2 (3).

However, in the presence of MIR1, the cell surface expression of both wild-type (wt) HLA.B7 and HLA.B7 2R was strongly down-regulated, even in cells expressing low levels of MIR1 (Fig. 1). In contrast, even high levels of MIR2 (Fig. 1) did not induce HLA.B7 2R down-regulation. Thus, the MIR1 protein can mediate the down-regulation of MHC I molecules lacking lysines. Similar results were observed in HeLa cells, suggesting that HLA.B7 2R down-regulation by MIR1 is not restricted to B cells. In the presence of MIR1, HLA.B7 2R molecules are endocytosed, translocated toward the lysosome, and degraded, which is similar to the effects of MIR1 on HLA.B7 wt molecules.

 Fig. 1.. MIR1, but not MIR2, down-regulates the MHC I allele HLA.B7 in the absence of intracytoplasmic lysines. BJAB cells stably expressing wt HLA.B7 or the HLA.B7 2R mutant lacking the two intracytoplasmic lysines were transiently transfected with a vector expressing MIR1 or MIR2 fused to enhanced green fluorescent protein (EGFP). Cells were stained with a phycoerythrin-conjugated monoclonal antibody against HLA.B7 and analyzed by flow cytometry. [View Larger Version of this Image (84K GIF file)]
To test whether a particular motif encoded in the intracytoplasmic domain of HLA.B7 2R was required for MIR1-mediated down-regulation, we generated a set of HLA.B7 2R molecules lacking different parts of the intracytoplasmic domain (Fig. 2A) and tested their susceptibility to MIR1-mediated down-regulation. Deletion of the last seven amino acids in HLA.B7 2R did not prevent down-regulation (HLA.B7 {Delta}C), whereas further truncations (constructs HLA.B7 {Delta}, {Delta}A, and {Delta}B) inhibited internalization (Fig. 2C). Thus, a critical determinant for MIR1-mediated down-regulation is encoded in the last seven residues of HLA.B7 {Delta}C.

 Fig. 2.. An intracytoplasmic cysteine residue is critical for lysine-independent down-regulation by MIR1. (A) Polymerase chain reaction (PCR) mutagenesis was used to create serial deletion mutants in the intracytoplasmic tail of HLA.B7 2R. (B) We generated several mutations within the intracytoplasmic region of HLA.B7 and HLA.A2 so as to analyze the requirement of the cysteine residue unique to HLA.B7. (C) BJAB cells stably expressing the mutants in (A) were transiently transfected with a construct expressing MIR1-EGFP and analyzed for surface expression of HLA.B7 by flow cytometry. (D) BJAB cells stably expressing MIR1-EGFP along with the various HLA.B7 mutants were analyzed for surface HLA.B7 expression by flow cytometry. (E) HeLa cells stably expressing MIR1-EGFP and various HLA.A2 mutants were analyzed for surface HLA.A2 expression. No down-regulation is indicated by cells stably expressing HLA.A2 and EGFP alone. [View Larger Version of this Image (33K GIF file)]
Although we observed down-regulation of lysineless HLA.B7 by MIR1, a lysine-less HLA.A2 molecule is not down-regulated by MIR1 (7). Within the region identified above, HLA.B7 encodes a cysteine in the same position that HLA.A2 encodes a serine (Fig. 2B). We generated a HLA.B7 mutant lacking both cysteine and lysine in its cytoplasmic tail, which we call HLA.B7 2RS (Fig. 2B). Mutation of the cysteine decreased the extent of MIR1-mediated endocytosis (Fig. 2D). We then introduced by mutagenesis a cysteine into the intracytoplasmic tail of HLA.A2 in which all the intracytoplasmic lysines were previously mutated (Fig. 2B). HLA.A2 without lysines (HLA A2 3R) was slightly down-regulated in the presence of MIR1, and introduction of the cysteine in HLA.A2 3R (HLA.A2 3RC) allowed full down-regulation (Fig. 2E). We also substituted the last arginine residue of HLA.B7 2RS (HLA.B7 without lysines or cysteines) with a cysteine and observed that this mutant was as susceptible as HLA.B7 wt to MIR1-mediated down-regulation (Fig. 2, B and D). This strongly suggested that the cysteine was not acting within a linear motif. Thus, in addition to the lysine- and Ub-dependent pathway, MIR1 can down-regulate surface molecules in a lysine-independent manner through a process that requires a cysteine in the intracytoplasmic tail of the target molecule. Other determinants may also be important, because HLA.B7 2RS and HLA.A2 3R, neither of which contains lysines or cysteines, are both partially down-regulated (Fig. 2, D and E).

To further demonstrate that a single cysteine was sufficient to promote MIR1-mediated down-regulation, we replaced the intracytoplasmic tail of HLA.B7 by a stretch of glycine and alanine residues (GA stretch) (Fig. 3A). To this GA stretch, we added each of the 20 amino acids at position X (Fig. 3B). As expected, the GA stretch did not allow down-regulation, whereas the presence of a lysine did. Thus, lysine is sufficient to promote ubiquitination-mediated down-regulation independent of surrounding motifs. The same phenotype was observed in the presence of a cysteine (Fig. 3B). None of the other amino acids lead to down-regulation in the presence of MIR1 (Fig. 3B), except serine. The extent of the down-regulation in the presence of a serine was modest but highly reproducible. This is consistent with the fact that HLA.B7 2R (which does not have lysines but has a cysteine) is strongly down-regulated, and HLA.B7 2RS (no lysines or cysteine) is partially down-regulated (Fig. 2D). Indeed, HLA.B7 2RS contains nine serine residues in its cytoplasmic tail. Overall, it appears that MHC I molecules can be down-regulated independently of lysines, in a cysteine-dependent (and possibly serine-dependent) fashion.

 Fig. 3.. One lysine or cysteine residue is sufficient to promote down-regulation of HLA.B7 by MIR1. (A) Amino acid sequence of the intracytoplasmic tail of HLA.B7 mutants where the tail has been replaced by a random GA stretch. Each of the 20 amino acids was substituted at position X. (B) BJAB cells stably expressing the HLA.B7 GA mutants were transfected with MIR1-EGFP and an EGFP control, then analyzed for surface expression of HLA.B7 using flow cytometry. [View Larger Version of this Image (32K GIF file)]
We examined the possibility that lysineless MHC I molecules could be ubiquitinated in the presence of MIR1. We used the hamster CHO cell line, which is permissive for MIR1-mediated down-regulation and does not express endogenous human MHC I molecules. We stably transduced CHO cells with the different HLA.B7 constructs and MIR1. After selection, human MHC I heavy chains were specifically immunoprecipitated, and their ubiquitination status was analyzed. No ubiquitinated forms were observed in the absence of MIR1, or when MIR1 was coexpressed with the HLA.B7 construct lacking almost all its intracytoplasmic domain, HLA.B7 {Delta} (Fig. 4A). However, in cells expressing MIR1, ubiquitination of HLA.B7 wt and, to a lesser extent, HLA.B7 2R (no lysines) was readily detectable, because it produced a characteristic heterogeneous array. In addition, a small but detectable degree of ubiquitination was observed in HLA.B7 2RS (no lysines or cysteine), consistent with the lower level of down-regulation observed (Fig. 4B). Thus, a residue other than lysine was being ubiquitinated by MIR1.

 Fig. 4.. A novel form of ubiquitination is detectable on HLA.B7 2R. (A) Lysates from CHO cells stably expressing wt HLA.B7, HLA.B7 2R, HLA.B7 2RS, and HLA.B7 {Delta} with or without stable expression of MIR1 were used in an immunoprecipitation reaction. The reaction was carried out using the antibody against human MHC I w6/32 (which recognizes only properly folded human MHC I molecules), and ubiquitinated species were detected by Western blot with an antibody against ubiquitin. (B) Lysates from CHO cells stably expressing wt HLA.B7 or HLA.B7 2R with MIR1 were immunoprecipitated with an antibody against MHC I, eluted in the presence of the reducing agent ß2-mercaptoethanol at either pH 8 or pH 11, and analyzed by Western blot using an antibody against ubiquitin. (C) WtHLA.B7 and HLA.B7 2R were immunoprecipitated as above, and the presence of HLA.B7 was determined by staining with the antibody against human MHC I, HC10. [View Larger Version of this Image (38K GIF file)]

We next examined the possibility that this cysteine was the ubiquitination site for HLA.B7 2R. We immunoprecipitated wt HLA.B7, as well as HLA.B7 2R, from CHO cells expressing MIR1, and we incubated these immunoprecipitates in the presence of ß2-mercaptoethanol at pH 11 in order to break potential thiol-ester bonds (cysteine-Ub bond) but not isopeptide bonds (lysine-Ub bond). Ubiquitination of HLA.B7 2R, but not HLA.B7 wt, was completely eliminated by this treatment (Fig. 4, B and C). Similarly, treatment drastically diminished the cysteine-Ub bond from the E2 enzyme UBE2E3 (fig. S1).

Altogether, our results show that in the absence of lysine, HLA.B7 molecules are ubiquitinated in a cysteine-dependent manner. Moreover, the bond between ubiquitin and the lysineless HLA.B7 shares the same chemical property as the bond between ubiquitin and E2s, which strongly suggests that cysteine is the ubiquitin-attachment site for HLA.B7 2R. Direct visualization of the cysteine-ubiquitin bond by mass spectrometry is hindered by the small amount of ubiquitinated molecules available for purification.

The foregoing shows that the side chain of residues other than lysine can serve as receptors for substrate ubiquitination. It is puzzling that, although ubiquitination has been extensively studied, in particular using large-scale proteomic, such a modification has never been observed in the past. A thiol-ester bond (cysteine-ubiquitin) is more labile than an isopeptide bond (lysine-ubiquitin), which certainly hinders its detection. This may explain why the level of ubiquitination detected with HLA.B7 2R is not as robust as the one observed with HLA.B7 wt (Fig. 4A). In addition, we believe that this form of ubiquitination might be restricted to a subfamily of E3 ubiquitin ligases, such as the MIR1 E3 ubiquitin ligase family (MIR1 and its homologs) (13) (SOM text and fig. S2). The regulation processes mediated by ubiquitination may be more complex because nonlysine residues are also targets of ubiquitination. For example, the number of potential substrates could be extended to molecules that do not contain accessible lysines or an accessible N terminus, and/or transient ubiquitination of substrates may occur, because thiolester bonds (Ub-cysteine) are more labile than isopeptide bonds (Ub-lysine). It will be important to determine whether this alternate form of ubiquitination requires the same cellular cofactors as the ones involved in lysine ubiquitination. The physiological relevance, for the virus, of this alternate form of ubiquitination is still unclear. An attractive hypothesis is that the ability of MIR1 to act on lysineless molecules allows it to broaden its potential targets.

References and Notes Back to Top

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Supporting Online Material

Materials and Methods

SOM Text

Figs. S1 and S2

Received for publication 27 January 2005. Accepted for publication 26 April 2005.

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Ube2j2 ubiquitinates hydroxylated amino acids on ER-associated degradation substrates.
X. Wang, R. A. Herr, M. Rabelink, R. C. Hoeben, E. J.H.J. Wiertz, and T. H. Hansen (2009)
J. Cell Biol. 187, 655-668
   Abstract »    Full Text »    PDF »
Molecular Mechanism of BST2/Tetherin Downregulation by K5/MIR2 of Kaposi's Sarcoma-Associated Herpesvirus.
M. Mansouri, K. Viswanathan, J. L. Douglas, J. Hines, J. Gustin, A. V. Moses, and K. Fruh (2009)
J. Virol. 83, 9672-9681
   Abstract »    Full Text »    PDF »
Functional Modulation of Dendritic Cells and Macrophages by Japanese Encephalitis Virus through MyD88 Adaptor Molecule-Dependent and -Independent Pathways.
A. G. Aleyas, J. A. George, Y. W. Han, M. M. Rahman, S. J. Kim, S. B. Han, B. S. Kim, K. Kim, and S. K. Eo (2009)
J. Immunol. 183, 2462-2474
   Abstract »    Full Text »    PDF »
LXR Regulates Cholesterol Uptake Through Idol-Dependent Ubiquitination of the LDL Receptor.
N. Zelcer, C. Hong, R. Boyadjian, and P. Tontonoz (2009)
Science 325, 100-104
   Abstract »    Full Text »    PDF »
Human Immunodeficiency Virus Type 1 Nef Protein Targets CD4 to the Multivesicular Body Pathway.
L. L. P. daSilva, R. Sougrat, P. V. Burgos, K. Janvier, R. Mattera, and J. S. Bonifacino (2009)
J. Virol. 83, 6578-6590
   Abstract »    Full Text »    PDF »
Adapter-mediated Substrate Selection for Endoplasmic Reticulum-associated Degradation.
K. Corcoran, X. Wang, and L. Lybarger (2009)
J. Biol. Chem. 284, 17475-17487
   Abstract »    Full Text »    PDF »
Polyubiquitination by HECT E3s and the Determinants of Chain Type Specificity.
H. C. Kim and J. M. Huibregtse (2009)
Mol. Cell. Biol. 29, 3307-3318
   Abstract »    Full Text »    PDF »
Ubiquitylation on Canonical and Non-canonical Sites Targets the Transcription Factor Neurogenin for Ubiquitin-mediated Proteolysis.
J. M. D. Vosper, G. S. McDowell, C. J. Hindley, C. S. Fiore-Heriche, R. Kucerova, I. Horan, and A. Philpott (2009)
J. Biol. Chem. 284, 15458-15468
   Abstract »    Full Text »    PDF »
Properties of the Ubiquitin-Pex5p Thiol Ester Conjugate.
C. P. Grou, A. F. Carvalho, M. P. Pinto, S. J. Huybrechts, C. Sa-Miranda, M. Fransen, and J. E. Azevedo (2009)
J. Biol. Chem. 284, 10504-10513
   Abstract »    Full Text »    PDF »
Analysis of nondegradative protein ubiquitylation with a monoclonal antibody specific for lysine-63-linked polyubiquitin.
H. Wang, A. Matsuzawa, S. A. Brown, J. Zhou, C. S. Guy, P.-H. Tseng, K. Forbes, T. P. Nicholson, P. W. Sheppard, H. Hacker, et al. (2008)
PNAS 105, 20197-20202
   Abstract »    Full Text »    PDF »
Urm1 at the crossroad of modifications.
P. G. A. Pedrioli, S. Leidel, and K. Hofmann (2008)
EMBO Rep. 9, 1196-1202
   Abstract »    Full Text »    PDF »
The N-terminal domain of MyoD is necessary and sufficient for its nuclear localization-dependent degradation by the ubiquitin system.
R. Sadeh, K. Breitschopf, B. Bercovich, M. Zoabi, Y. Kravtsova-Ivantsiv, D. Kornitzer, A. Schwartz, and A. Ciechanover (2008)
PNAS 105, 15690-15695
   Abstract »    Full Text »    PDF »
Remodeling of Endothelial Adherens Junctions by Kaposi's Sarcoma-Associated Herpesvirus.
M. Mansouri, P. P. Rose, A. V. Moses, and K. Fruh (2008)
J. Virol. 82, 9615-9628
   Abstract »    Full Text »    PDF »
The Varicellovirus UL49.5 Protein Blocks the Transporter Associated with Antigen Processing (TAP) by Inhibiting Essential Conformational Transitions in the 6+6 Transmembrane TAP Core Complex.
M. C. Verweij, D. Koppers-Lalic, S. Loch, F. Klauschies, H. de la Salle, E. Quinten, P. J. Lehner, A. Mulder, M. R. Knittler, R. Tampe, et al. (2008)
J. Immunol. 181, 4894-4907
   Abstract »    Full Text »    PDF »
Members of the E2D (UbcH5) Family Mediate the Ubiquitination of the Conserved Cysteine of Pex5p, the Peroxisomal Import Receptor.
C. P. Grou, A. F. Carvalho, M. P. Pinto, S. Wiese, H. Piechura, H. E. Meyer, B. Warscheid, C. Sa-Miranda, and J. E. Azevedo (2008)
J. Biol. Chem. 283, 14190-14197
   Abstract »    Full Text »    PDF »
APOBEC3G Is Degraded by the Proteasomal Pathway in a Vif-dependent Manner without Being Polyubiquitylated.
Y. Dang, L. M. Siew, and Y.-H. Zheng (2008)
J. Biol. Chem. 283, 13124-13131
   Abstract »    Full Text »    PDF »
The Specificities of Kaposi's Sarcoma-Associated Herpesvirus-Encoded E3 Ubiquitin Ligases Are Determined by the Positions of Lysine or Cysteine Residues within the Intracytoplasmic Domains of Their Targets.
K. Cadwell and L. Coscoy (2008)
J. Virol. 82, 4184-4189
   Abstract »    Full Text »    PDF »
Activation of CXCR4 Triggers Ubiquitination and Down-regulation of Major Histocompatibility Complex Class I (MHC-I) on Epithelioid Carcinoma HeLa Cells.
Z. Wang, L. Zhang, A. Qiao, K. Watson, J. Zhang, and G.-H. Fan (2008)
J. Biol. Chem. 283, 3951-3959
   Abstract »    Full Text »    PDF »
Down-regulation of NKG2D and NKp80 ligands by Kaposi's sarcoma-associated herpesvirus K5 protects against NK cell cytotoxicity.
M. Thomas, J. M. Boname, S. Field, S. Nejentsev, M. Salio, V. Cerundolo, M. Wills, and P. J. Lehner (2008)
PNAS 105, 1656-1661
   Abstract »    Full Text »    PDF »
Apoptosis induction by Bid requires unconventional ubiquitination and degradation of its N-terminal fragment.
S. W.G. Tait, E. de Vries, C. Maas, A. M. Keller, C. S. D'Santos, and J. Borst (2007)
J. Cell Biol. 179, 1453-1466
   Abstract »    Full Text »    PDF »
Dislocation of an Endoplasmic Reticulum Membrane Glycoprotein Involves the Formation of Partially Dislocated Ubiquitinated Polypeptides.
B. M. Baker and D. Tortorella (2007)
J. Biol. Chem. 282, 26845-26856
   Abstract »    Full Text »    PDF »
A Conserved Cysteine Is Essential for Pex4p-dependent Ubiquitination of the Peroxisomal Import Receptor Pex5p.
C. Williams, M. van den Berg, R. R. Sprenger, and B. Distel (2007)
J. Biol. Chem. 282, 22534-22543
   Abstract »    Full Text »    PDF »
Ubiquitination of serine, threonine, or lysine residues on the cytoplasmic tail can induce ERAD of MHC-I by viral E3 ligase mK3.
X. Wang, R. A. Herr, W.-J. Chua, L. Lybarger, E. J.H.J. Wiertz, and T. H. Hansen (2007)
J. Cell Biol. 177, 613-624
   Abstract »    Full Text »    PDF »
Ubiquitin, Hormones and Biotic Stress in Plants.
K. Dreher and J. Callis (2007)
Ann. Bot. 99, 787-822
   Abstract »    Full Text »    PDF »
Seven-Transmembrane Receptors and Ubiquitination.
S. K. Shenoy (2007)
Circ. Res. 100, 1142-1154
   Abstract »    Full Text »    PDF »
Degrons at the C Terminus of the Pathogenic but Not the Nonpathogenic Hantavirus G1 Tail Direct Proteasomal Degradation.
N. Sen, A. Sen, and E. R. Mackow (2007)
J. Virol. 81, 4323-4330
   Abstract »    Full Text »    PDF »
Downregulation of Gamma Interferon Receptor 1 by Kaposi's Sarcoma-Associated Herpesvirus K3 and K5.
Q. Li, R. Means, S. Lang, and J. U. Jung (2007)
J. Virol. 81, 2117-2127
   Abstract »    Full Text »    PDF »
Decoding ubiquitin sorting signals for clathrin-dependent endocytosis by CLASPs.
L. M. Traub and G. L. Lukacs (2007)
J. Cell Sci. 120, 543-553
   Abstract »    Full Text »    PDF »
Proteasome-Independent Functions of Ubiquitin in Endocytosis and Signaling.
D. Mukhopadhyay and H. Riezman (2007)
Science 315, 201-205
   Abstract »    Full Text »    PDF »
Kaposi sarcoma herpesvirus K5 removes CD31/PECAM from endothelial cells.
M. Mansouri, J. Douglas, P. P. Rose, K. Gouveia, G. Thomas, R. E. Means, A. V. Moses, and K. Fruh (2006)
Blood 108, 1932-1940
   Abstract »    Full Text »    PDF »
A Novel Family of Membrane-Bound E3 Ubiquitin Ligases.
M. Ohmura-Hoshino, E. Goto, Y. Matsuki, M. Aoki, M. Mito, M. Uematsu, H. Hotta, and S. Ishido (2006)
J. Biochem. 140, 147-154
   Abstract »    Full Text »    PDF »
Kaposi's sarcoma-associated herpesvirus immune modulation: an overview.
S. A. R. Rezaee, C. Cunningham, A. J. Davison, and D. J. Blackbourn (2006)
J. Gen. Virol. 87, 1781-1804
   Abstract »    Full Text »    PDF »
Inhibition of MHC Class II Expression and Immune Responses by c-MIR.
M. Ohmura-Hoshino, Y. Matsuki, M. Aoki, E. Goto, M. Mito, M. Uematsu, T. Kakiuchi, H. Hotta, and S. Ishido (2006)
J. Immunol. 177, 341-354
   Abstract »    Full Text »    PDF »
The Viral E3 Ubiquitin Ligase mK3 Uses the Derlin/p97 Endoplasmic Reticulum-associated Degradation Pathway to Mediate Down-regulation of Major Histocompatibility Complex Class I Proteins.
X. Wang, Y. Ye, W. Lencer, and T. H. Hansen (2006)
J. Biol. Chem. 281, 8636-8644
   Abstract »    Full Text »    PDF »
A Bacterial Inhibitor of Host Programmed Cell Death Defenses Is an E3 Ubiquitin Ligase.
R. Janjusevic, R. B. Abramovitch, G. B. Martin, and C. E. Stebbins (2006)
Science 311, 222-226
   Abstract »    Full Text »    PDF »
Viral strategies for evading antiviral cellular immune responses of the host.
A. Iannello, O. Debbeche, E. Martin, L. H. Attalah, S. Samarani, and A. Ahmad (2006)
J. Leukoc. Biol. 79, 16-35
   Abstract »    Full Text »    PDF »

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