Identification of RPS14 as a 5q- syndrome gene by RNA interference screen

Somatic chromosomal deletions in cancer are thought to indicate the location of tumour suppressor genes, by which a complete loss of gene function occurs through biallelic deletion, point mutation or epigenetic silencing, thus fulfilling Knudson's two-hit hypothesis. In many recurrent deletions, however, such biallelic inactivation has not been found. One prominent example is the 5q- syndrome, a subtype of myelodysplastic syndrome characterized by a defect in erythroid differentiation. Here we describe an RNA-mediated interference (RNAi)-based approach to discovery of the 5q- disease gene. We found that partial loss of function of the ribosomal subunit protein RPS14 phenocopies the disease in normal haematopoietic progenitor cells, and also that forced expression of RPS14 rescues the disease phenotype in patient-derived bone marrow cells. In addition, we identified a block in the processing of pre-ribosomal RNA in RPS14-deficient cells that is functionally equivalent to the defect in Diamond-Blackfan anaemia, linking the molecular pathophysiology of the 5q- syndrome to a congenital syndrome causing bone marrow failure. These results indicate that the 5q- syndrome is caused by a defect in ribosomal protein function and suggest that RNAi screening is an effective strategy for identifying causal haploinsufficiency disease genes.     

A threshold model for the French franc/deutschmark exchange rate

The behaviour of the French franc/deutschmark exchange rate is examined in this paper. During the time period studied, these currencies were constrained to lie within prescribed bands relative to one another and the usual random walk explanation of the exchange rate may not be appropriate. The data are examined for evidence of non-linear structure and it is shown that a piecewise linear SETAR model provides a better explanation and superior forecasting performance than a random walk.     

Structure of a RING E3 ligase and ubiquitin-loaded E2 primed for catalysis

Ubiquitin modification is mediated by a large family of specificity determining ubiquitin E3 ligases. To facilitate ubiquitin transfer, RING E3 ligases bind both substrate and a ubiquitin E2 conjugating enzyme linked to ubiquitin via a thioester bond, but the mechanism of transfer has remained elusive. Here we report the crystal structure of the dimeric RING domain of rat RNF4 in complex with E2 (UbcH5A) linked by an isopeptide bond to ubiquitin. While the E2 contacts a single protomer of the RING, ubiquitin is folded back onto the E2 by contacts from both RING protomers. The carboxy-terminal tail of ubiquitin is locked into an active site groove on the E2 by an intricate network of interactions, resulting in changes at the E2 active site. This arrangement is primed for catalysis as it can deprotonate the incoming substrate lysine residue and stabilize the consequent tetrahedral transition-state intermediate.     

Sequence of protein disulphide isomerase and implications of its relationship to thioredoxin

The formation of disulphide bonds is essential to the structure and function of proteins. These bonds rapidly form either cotranslationally or immediately post-translationally in the lumen of the endoplasmic reticulum. Native disulphide pairing for such proteins has been achieved in vitro; however, the rates of reassembly are slow and the conditions non-physiological. To account for these observations, Anfinsen et al. proposed that a 'disulphide interchange protein' was the in vivo catalyst of disulphide bond rearrangement. Other groups discovered an activity with similar characteristics that catalysed the reductive cleavage of insulin and may be associated with insulin degradation, although this result has been disputed. The enzyme involved, protein disulphide isomerase (PDI; EC 5.3.4.1), may be the in vivo catalyst of disulphide bond formation. Here we describe the sequence of cloned rat liver PDI complementary DNA which predicts a protein with two distinct regions homologous with Escherichia coli thioredoxin, a known cofactor in oxidation-reduction reactions. Each of these regions contains the presumed active site sequence Trp-Cys-Gly-His-Cys-Lys, suggesting that PDI, similar in action to thioredoxin, catalyses disulphide bond interchange via an internal disulphide-sulphydryl interchange. The cDNA predicts a signal peptide consistent with the view that PDI is a luminal endoplasmic reticulum protein. PDI messenger RNA, although ubiquitous, is more highly concentrated in secretory cells.     

Melanin-concentrating hormone is the cognate ligand for the orphan G-protein-coupled receptor SLC-1.

The underlying causes of obesity are poorly understood but probably involve complex interactions between many neurotransmitter and neuropeptide systems involved in the regulation of food intake and energy balance. Three pieces of evidence indicate that the neuropeptide melanin-concentrating hormone (MCH) is an important component of this system. First, MCH stimulates feeding when injected directly into rat brains; second, the messenger RNA for the MCH precursor is upregulated in the hypothalamus of genetically obese mice and in fasted animals; and third, mice lacking MCH eat less and are lean. MCH antagonists might, therefore, provide a treatment for obesity. However, the development of such molecules has been hampered because the identity of the MCH receptor has been unknown until now. Here we show that the 353-amino-acid human orphan G-protein-coupled receptor SLC-1 expressed in HEK293 cells binds MCH with sub-nanomolar affinity, and is stimulated by MCH to mobilize intracellular Ca2+ and reduce forskolin-elevated cyclic AMP levels. We also show that SLC-1 messenger RNA and protein is expressed in the ventromedial and dorsomedial nuclei of the hypothalamus, consistent with a role for SLC-1 in mediating the effects of MCH on feeding.