Global mRNA degradation during lytic gammaherpesvirus infection contributes to establishment of viral latency.

During a lytic gammaherpesvirus infection, host gene expression is severely restricted by the global degradation and altered 3' end processing of mRNA. This host shutoff phenotype is orchestrated by the viral SOX protein, yet its functional significance to the viral lifecycle has not been elucidated, in part due to the multifunctional nature of SOX. Using an unbiased mutagenesis screen of the murine gammaherpesvirus 68 (MHV68) SOX homolog, we isolated a single amino acid point mutant that is selectively defective in host shutoff activity.

Suppression of TLR9 immunostimulatory motifs in the genome of a gammaherpesvirus.

Multiple receptors within the innate immune system have evolved to recognize nucleic acids as signatures of viral infection. It is believed that this specificity is essential for viral detection, as viruses often lack other invariant features that can serve as suitable targets for innate receptors. One such innate receptor, TLR9, has been implicated in the detection of many dsDNA viruses.

Modulation of a P-TEFb functional equilibrium for the global control of cell growth and differentiation.

P-TEFb phosphorylates RNA polymerase II and negative elongation factors to stimulate general transcriptional elongation. It is kept in a functional equilibrium through alternately interacting with its positive (the Brd4 protein) and negative (the HEXIM1 protein and 7SK snRNA) regulators. To investigate the physiological significance of this phenomenon, we analyzed the responses of HeLa cells and murine erythroleukemia cells (MELC) to hexamethylene bisacetamide (HMBA), which inhibits growth and induces differentiation of many cell types.

Compensatory contributions of HEXIM1 and HEXIM2 in maintaining the balance of active and inactive positive transcription elongation factor b complexes for control of transcription.

Human positive transcriptional elongation factor b (P-TEFb), consisting of a cyclin-dependent kinase 9-cyclin T heterodimer, stimulates general and disease-specific transcriptional elongation by phosphorylating RNA polymerase II. The HEXIM1 protein, aided by the 7SK snRNA, sequesters P-TEFb into an inactive 7SK.HEXIM1.

A human immunodeficiency virus type 1 Tat-like arginine-rich RNA-binding domain is essential for HEXIM1 to inhibit RNA polymerase II transcription through 7SK snRNA-mediated inactivation of P-TEFb.

The HEXIM1 protein inhibits the kinase activity of P-TEFb (CDK9/cyclin T) to suppress RNA polymerase II transcriptional elongation in a process that specifically requires the 7SK snRNA, which mediates the interaction of HEXIM1 with P-TEFb. In an attempt to define the sequence requirements for HEXIM1 to interact with 7SK and inactivate P-TEFb, we have identified the first 18 amino acids within the previously described nuclear localization signal (NLS) of HEXIM1 as both necessary and sufficient for binding to 7SK in vivo and in vitro. This 7SK-binding motif was essential for HEXIM1's inhibitory action, as the HEXIM1 mutants with this motif replaced with a foreign NLS failed to interact with 7SK and P-TEFb and hence were unable to inactivate P-TEFb.