1. The M2 protein of influenza A virus is implicated in transmembrane pH regulation during infection. Whole-cell patch clamp of mouse erythroleukaemia cells expressing the M2 protein in the surface membrane showed a conductance due to M2 which was specifically blocked by the anti-influenza drug rimantadine. 2. The ion selectivity of the rimantadine-sensitive current through M2 was determined.Reversal potentials were close to equilibrium potentials for transmembrane pH gradients and not to those for Na+, K+ or Cl-concentration gradients. M2 permeability to Na+ relative to H+ was estimated to be less than 6 x 10-7.3. The M2 conductance increased as external pH decreased below 8X5 and approached saturation at an external pH of 4, effects attributable to increased permeability due to increased driving potential and to activation by low external pH. Both activation and permeation could be described by interaction of protons with sites on M2, with apparent dissociation constants of approximately 0.1 /SM and 1 /SM, respectively, under physiological conditions.4. The M2 protein can transfer protons selectively across membranes with the H+ electrochemical gradient, properties consistent with its role in modifying virion and trans-

The human beta‐globin dominant control region (DCR) was previously identified as a region from the 5′ end of the human beta‐globin locus which directs high level, site of integration‐independent, copy number‐dependent expression on a linked human beta‐globin gene in transgenic mice and stably transfected mouse erythroleukaemia (MEL) cells. We have now analysed the elements comprising the DCR by systematic deletion mutagenesis in stable MEL transfectants. We have identified two independent elements within the DNase I hypersensitive sites 2 and 3, containing fragments which direct strong transcriptional inducibility of a beta‐globin gene. Whilst the remaining two hypersensitive sites do not direct significant transcriptional induction, our data suggest that all four sites may be necessary for the fully regulated expression conferred by the DCR. We have also tested a number of beta‐globin minigene constructs under the control of the DCR to assess if any of the local sequences from the gene may be removed without loss of expression. We find that the 3′ enhancer may be removed without affecting expression, but there is an absolute requirement for the presence of the second intron, not related to the enhancer present in that intron.

We describe here for the first time the site of retention within the nucleus of pre-mRNA processing mutants unable to be exported to the cytoplasm. Fluorescence in situ hybridization was used to detect transcripts from human β-globin genes that are either normal or defective in splicing or 3Ј end formation. Nuclear transcripts of both wild-type and mutant RNAs are detected only as intranuclear foci that colocalize with the template gene locus. The kinetics of transcript release from the site of transcription was assessed by treatment of cells with the transcriptional inhibitors actinomycin D, α-amanitin and DRB. These drugs induce the rapid disappearance of nuclear foci corresponding to wild-type human β-globin RNA. In contrast, pre-mRNA mutants defective in either splicing or 3Ј end formation and which fail to be transported to the cytoplasm, are retained at the site of transcription. Therefore, 3Ј end processing and splicing appear to be rate limiting for release of mRNA from the site of transcription.

The regulatory elements that determine the expression pattern of a number of eukaryotic genes expressed specifically in certain tissues have been defined and studied in detail. In general, however, the expression conferred by these elements on genes reintroduced into the genomes of cell lines and transgenic animals has turned out to be at a low level relative to that of endogenous genes, and influenced by the chromosomal site of insertion of the exogenous construct. We have previously shown that if regions flanking the human beta-globin locus are introduced into the mouse genome along with the human beta-globin gene, a level of expression comparable to that of endogenous genes can be achieved that is also independent of integration site. We have now defined a dominant control region with these properties consisting of 6.5 kilobases of DNA encompassing erythroid cell-specific DNase I hypersensitive sites. The identification of such dominant control regions could have important applications in somatic gene therapy.

The protein factor U2 snRNP Auxiliary Factor (U2AF) 65 is an essential component required for splicing and involved in the coupling of splicing and 3 0 end processing of vertebrate pre-mRNAs. Here we have addressed the mechanisms by which U2AF 65 stimulates pre-mRNA 3 0 end processing. We identify an arginine/serine-rich region of U2AF 65 that mediates an interaction with an RS-like alternating charge domain of the 59 kDa subunit of the human cleavage factor I (CF I m ), an essential 3 0 processing factor that functions at an early step in the recognition of the 3 0 end processing signal. Tethered functional analysis shows that the U2AF 65/CF I m 59 interaction stimulates in vitro 3 0 end cleavage and polyadenylation. These results therefore uncover a direct role of the U2AF 65/CF I m 59 interaction in the functional coordination of splicing and 3 0 end processing.

Huntington's disease is an inherited neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. The peripheral innate immune system contributes to Huntington's disease pathogenesis and has been targeted successfully to modulate disease progression, but mechanistic understanding relating this to mutant huntingtin expression in immune cells has been lacking. Here we demonstrate that human Huntington's disease myeloid cells produce excessive inflammatory cytokines as a result of the cell-intrinsic effects of mutant huntingtin expression. A direct effect of mutant huntingtin on the NFκB pathway, whereby it interacts with IKKγ, leads to increased degradation of IκB and subsequent nuclear translocation of RelA. Transcriptional alterations in intracellular immune signalling pathways are also observed. Using a novel method of small interfering RNA delivery to lower huntingtin expression, we show reversal of disease-associated alterations in cellular function-the first time this has been demonstrated in primary human cells. Glucan-encapsulated small interfering RNA particles were used to lower huntingtin levels in human Huntington's disease monocytes/macrophages, resulting in a reversal of huntingtin-induced elevated cytokine production and transcriptional changes. These findings improve our understanding of the role of innate immunity in neurodegeneration, introduce glucan-encapsulated small interfering RNA particles as tool for studying cellular pathogenesis ex vivo in human cells and raise the prospect of immune cell-directed HTT-lowering as a therapeutic in Huntington's disease.

Gene therapy for ␤-thalassemia requires stable transfer of a ␤-globin gene into hematopoietic stem cells (HSCs) and high and regulated hemoglobin expression in the erythroblastic progeny. We developed an erythroid-specific lentiviral vector driving the expression of the human ␤-globin gene from a minimal promoter/enhancer element containing two hypersensitive sites from the ␤-globin locus control region. Transplantation of transduced HSCs into thalassemic mice leads to stable and long-term correction of anemia with all red blood cells expressing the transgene. A frequency of 30 -50% of transduced HSCs, harboring an average vector copy number per cell of 1, was sufficient to fully correct the thalassemic phenotype. In the mouse model of Cooley's anemia transplantation of transduced cells rescues lethality, leading to either a normal or a thalassemia intermedia phenotype. We show that genetically corrected erythroblasts undergo in vivo selection with preferential survival of progenitors harboring proviral integrations in genome sites more favorable to high levels of vector-derived expression. These data provide a rationale for a gene therapy approach to ␤-thalassemia based on partially myeloablative transplantation protocols.gene therapy ͉ hematopoietic stem cells ͉ lentiviral vector

Ubiquitously acting chromatin opening elements (UCOEs) consist of methylation-free CpG islands encompassing dual divergently transcribed promoters of housekeeping genes that have been shown to confer resistance to transcriptional silencing and to produce consistent and stable transgene expression in tissue culture systems. To develop improved strategies for hematopoietic cell gene therapy, we have assessed the potential of the novel human HNRPA2B1-CBX3 UCOE (A2UCOE) within the context of a self-inactivating (SIN) lentiviral vector. Unlike viral promoters, the enhancer-less A2UCOE gave rise to populations of cells that expressed a reporter transgene at a highly reproducible level. The efficiency of expression per vector genome was also markedly increased in vivo compared with vectors incorporating either spleen focus-forming virus (SFFV) or cytomegalovirus (CMV) promoters, suggesting a relative resistance to silencing. Furthermore, an A2UCOE-IL2RG vector fully restored the IL-2 signaling pathway within IL2RG-deficient human cells in vitro and successfully rescued the X-linked severe combined immunodeficiency (SCID-X1) phenotype in a mouse model of this disease. These data indicate that the A2UCOE displays highly reliable transcriptional activity within a lentiviral vector, largely overcoming insertion-site position effects and giving rise to therapeutically relevant levels of gene expression. These properties are achieved in the absence of classic enhancer activity and therefore may confer a high safety profile.