Monoubiquitinated histone H2B plays multiple roles in transcription activation. H2B is deubiquitinated by the Spt-Ada-Gcn5 acetyltransferase (SAGA) coactivator, which contains a four-protein subcomplex known as the deubiquitinating (DUB) module. The crystal structure of the Ubp8/Sgf11/Sus1/Sgf73 DUB module bound to a ubiquitinated nucleosome reveals that the DUB module primarily contacts H2A/H2B, with an arginine cluster on the Sgf11 zinc finger domain docking on the conserved H2A/H2B acidic patch. The Ubp8 catalytic domain mediates additional contacts with H2B, as well as with the conjugated ubiquitin. We find that the DUB module deubiquitinates H2B both in the context of the nucleosome and in H2A/H2B dimers complexed with the histone chaperone, FACT, suggesting that SAGA could target H2B at multiple stages of nucleosome disassembly and reassembly during transcription.

The interferon (IFN)-related cytokine interleukin (IL)-

Cytomegalovirus (CMV) is considered the most common infectious agent causing permanent neurological dysfunction in the developing brain. We have previously shown that CMV infects developing brain cells more easily than it infects mature brain cells and that this preference is independent of the host B-and T-cell responses. In the present study, we examined the innate antiviral defenses against mouse (m) and human ( Cytomegalovirus (CMV), a double-stranded DNA virus of the betaherpesvirus family, is considered the most common infectious agent that causes permanent neurological dysfunction of the developing brain (2, 62). Human CMV (hCMV) infections in the developing brain can lead to mental retardation, epilepsy, microcephaly, microgyria, hydrocephalus, and deafness (4, 21, 37). The developing brain is particularly sensitive to CMV infection (6,29,54,55,58) due to both the immature state of the systemic immune system and a preference of CMV for developing glia and neurons (61). CMV in the mature brain is less of a concern, except in immunocompromised individuals (22,23,32).Outside the brain, interferon (IFN) has been reported to limit some CMV infections (27,30,66). A number of reports have suggested that brain cells differ from cells of other organs relative to innate and systemic antiviral immune responses. The brain has some characteristics of an immunologically privileged region. For instance, although most cells outside the brain express major histocompatibility complex (MHC) class I molecules, neurons in the brain either do not express MHC class I or do so at a substantially reduced level (45). This may be beneficial due to the fact that neurons do not replicate, and so a vigorous attack by the immune system on virally infected postmitotic neurons may cause more problems than the virus itself. In the brain, functional receptors for IFN-␥ are expressed in all cells, but they are expressed at different levels, and actions of IFN-␣/␤ on microglia, astrocytes, and neurons have also been described (12,13,31,43). Most cells, including astrocytes and microglia, are able to produce IFN-␣/␤ as an initial nonspecific immune response against virus infection (52, 64); IFN-␥ is released by activated T lymphocytes as part of the specific immune response. The intrinsic IFN system provides the first line of defense against viral infections, including systemic CMV infections, and can delay viral replication allowing the activation of the systemic adaptive immune responses.One explanation for the increased pathogenesis in the developing brain compared to that in the mature brain is that the systemic immune system is too immature during development to fight CMV infection. T and B lymphocytes of the adaptive immune system, as well as other cells of the systemic immune system, including natural killer cells and macrophages/monocytes, are involved in combating CMV infections (2,5,8,9,10,20,46,49), and the efficacies of these systems increase with development. Another mechanism that might underlie the susceptibility of developing...

Pharmacological modulation of cellular proteins as a means to block virus replication has been proposed as an alternative antiviral strategy that may be less susceptible than others to the development of viral drug resistance. Recent evidence indicates that the ubiquitin-proteasome pathway interacts with different aspects of the hepatitis B virus (HBV) life cycle in cell culture models of virus replication. We therefore examined the effect of proteasome inhibition on HBV replication in vivo using HBV transgenic mice. The proteasome inhibitor bortezomib (Velcade) inhibits proteasome activity in vivo and is used therapeutically for the clinical treatment of multiple myeloma. We found that a single intravenous dose of 1 mg of bortezomib/kg of body weight reduced virus replication for as long as 6 days. The inhibition of HBV by bortezomib was dose dependent and occurred at a step in replication subsequent to viral RNA and protein expression. The reduction in HBV replication did not result from nonspecific hepatocellular toxicity and was not mediated indirectly through the induction of an intrahepatic interferon response. Thus, pharmacological manipulation of the ubiquitinproteasome pathway may represent an alternative therapeutic approach for the treatment of chronic HBV infection.

The type III interferon (IFN) family elicits an antiviral response that is nearly identical to that evoked by IFN-α/β. However, these cytokines (known as IFN-λ1, 2, and 3) signal through a distinct receptor, and thus may be resistant to the evasion strategies used by some viruses to avoid the IFN-α/β response. Orthopoxviruses are highly resistant to IFN-α/β because they encode well-characterized immunomodulatory proteins that inhibit IFN activity. These include a secreted receptor (B18R) that neutralizes IFN-α/β, and a cytoplasmic protein (E3L) that blocks IFN-α/β effector functions in infected cells. We therefore determined the ability of these immunomodulators to abrogate the IFN-λ-induced antiviral response. We found that (i) vaccinia virus (VACV) replication is resistant to IFN-λ antiviral activity; (ii) neither VACV B18R nor the variola virus homolog B20R neutralizes IFN-λ; (iii) VACV E3L inhibits the IFN-λ-mediated antiviral response through a PKR-dependent pathway; (iv) VACV infection inhibits IFN-λR-mediated signal transduction and gene expression. These results demonstrate differential sensitivity of IFN-λ to multiple distinct evasion mechanisms employed by a single virus.

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