Mapping of the protein import machinery in the mitochondrial outer membrane by crosslinking of translocation intermediates.

Mitochondria contain a complex machinery for the import of nuclear-encoded proteins. Receptor proteins exposed on the outer membrane surface are required for the specific binding of precursor proteins to mitochondria, either by binding of cytosolic signal recognition factors or by direct recognition of the precursor polypeptides. Subsequently, the precursors are inserted into the outer membrane at the general insertion site GIP (general insertion protein). Here we report the analysis of receptors and GIP by crosslinking of translocation intermediates and by coimmunoprecipitation. Surface-accumulated precursors were crosslinked to the receptors MOM19 and MOM72, suggesting a direct interaction of preproteins with surface receptors. We identified three novel mitochondrial outer membrane proteins, MOM7, MOM8, and MOM30 that, together with the previously identified MOM38, seem to form the GIP site and are present in the mitochondrial receptor complex.     

Close linkage of glucokinase locus on chromosome 7p to early-onset non-insulin-dependent diabetes mellitus.

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem, affecting 5% of the world population. Genetic factors are important in NIDDM, but the mechanisms leading to glucose intolerance are unknown. Genetic linkage has been investigated in multigeneration families to localize, and ultimately identify, the gene(s) predisposing to NIDDM. Here we report linkage between the glucokinase locus on chromosome 7p and diabetes in 16 French families with maturity-onset diabetes of the young, a form of NIDDM characterized by monogenic autosomal dominant transmission and early age of onset. Statistical evidence of genetic heterogeneity was significant, with an estimated 45-95% of the 16 families showing linkage to glucokinase. Because glucokinase is a key enzyme of blood glucose homeostasis, these results are evidence that a gene involved in glucose metabolism could be implicated in the pathogenesis of NIDDM.     

Otavipithecus namibiensis, first Miocene hominoid from southern Africa.

We report here the discovery of a Miocene hominoid from Berg Aukas, Namibia, the first known from the African continent south of equatorial East Africa. This represents a major range extension of Miocene Hominoidea in Africa to latitude 20 degrees S. The holotype, a right mandibular corpus preserving the crowns of the P4-M3, partial crown and root of the P3, partial root of the canine, alveoli for all four incisors, and partial alveolus for the left canine, was found during paleontological explorations of karst-fill breccias in the Otavi region of northern Namibia. The mandible has unique characteristics that differentiate it from other middle Miocene hominoids of Africa and Eurasia and represents the only fossil evidence documenting a pre-australopithecine stage of hominoid evolution in southern Africa. Faunal analyses indicate that the breccia block containing the specimen accumulated during the latter part of the middle Miocene, about 13 +/- 1 Myr. Fauna from other breccia blocks at Berg Aukas are of diverse ages, including the earlier part of the middle Miocene, the upper Miocene, Plio-Pleistocene and Holocene.     

A human recombinant haemoglobin designed for use as a blood substitute.

The need to develop a blood substitute is now urgent because of the increasing concern over blood-transmitted viral and bacterial pathogens. Cell-free haemoglobin solutions and human haemoglobin synthesized in Escherichia coli and Saccharomyces cerevisiae have been investigated as potential oxygen-carrying substitutes for red blood cells. But these haemoglobins cannot be used as a blood substitute because (1) the oxygen affinity in the absence of 2,3-bisphosphoglycerate is too high to allow unloading of enough oxygen in the tissues, and (2) they dissociate into alpha beta dimers that are cleared rapidly by renal filtration, which can result in long-term kidney damage. We have produced a human haemoglobin using an expression vector containing one gene encoding a mutant beta-globin with decreased oxygen affinity and one duplicated, tandemly fused alpha-globin gene. Fusion of the two alpha-globin subunits increases the half-life of this haemoglobin molecule in vivo by preventing its dissociation into alpha beta dimers and therefore also eliminates renal toxicity.     

Fusarium solani cutinase is a lipolytic enzyme with a catalytic serine accessible to solvent.

Lipases belong to a class of esterases whose activity on triglycerides is greatly enhanced at lipid-water interfaces. This phenomenon, called interfacial activation, has a structural explanation: a hydrophobic lid, which at rest covers the catalytic site, is displaced on substrate or inhibitor binding and probably interacts with the lipid matrix. Fusarium solani pisi cutinase belongs to a group of homologous enzymes of relative molecular mass 22-25K (ref. 7) capable of degrading cutin, the insoluble lipid-polyester matrix covering the surface of plants, and hydrolysing triglycerides. Cutinases differ from classical lipases in that they do not exhibit interfacial activation; they are active on soluble as well as on emulsified triglycerides. Cutinases therefore establish a bridge between esterases and lipases. We report here the three-dimensional structure of a recombinant cutinase from F. solani pisi, expressed in Escherichia coli. Cutinase is an alpha-beta protein; the active site is composed of the triad Ser 120, His 188 and Asp 175. Unlike other lipases, the catalytic serine is not buried under surface loops, but is accessible to solvent. This could explain why cutinase does not display interfacial activation.     

Tumour necrosis factor alpha restores granulomas and induces parasite egg-laying in schistosome-infected SCID mice.

Schistosomiasis (bilharzia) is a parasitic disease caused by several species of schistosome worms (blood flukes). The key pathogenic event in this disease is the formation of granulomas around schistosome eggs trapped in portal venules of the liver. Granulomas are a distinctive form of chronic inflammation characterized by localized aggregation of activated macrophages around an inciting stimulus. Each granuloma evolves to form a fibrous scar; in schistosomiasis, the result is widespread hepatic fibrosis and portal hypertension. To identify the specific immune signal molecules necessary for granuloma formation, we studied schistosome infections in severe combined immunodeficient (SCID) mice, which have normal macrophages but lack functional B or T lymphocytes. Here we report that the immunoregulatory cytokine tumour necrosis factor alpha is necessary and sufficient to reconstitute granuloma formation in schistosome-infected SCID mice. Moreover, we find that the parasitic worms require tumour necrosis factor alpha for egg-laying and for excretion of eggs from the host. The implication of this latter result is that the parasite has adapted so successfully to its host that it uses a host-derived immunoregulatory protein as a signal for replication and transmission.     

Human infection by genetically diverse SIVSM-related HIV-2 in west Africa.

Our understanding of the biology and origins of human immunodeficiency virus type 2 (HIV-2) derives from studies of cultured isolates from urban populations experiencing epidemic infection and disease. To test the hypothesis that such isolates might represent only a subset of a larger, genetically more diverse group of viruses, we used nested polymerase chain reactions to characterize HIV-2 sequences in uncultured mononuclear blood cells of two healthy Liberian agricultural workers, from whom virus isolation was repeatedly unsuccessful, and from a culture-positive symptomatic urban dweller. Analysis of pol, env and long terminal repeat regions revealed the presence of three highly divergent HIV-2 strains, one of which (from one of the healthy subjects) was significantly more closely related to simian immunodeficiency viruses infecting sooty mangabeys and rhesus macaques (SIVSM/SIVMAC) than to any virus of human derivation. This subject also harboured multiply defective viral genotypes that resulted from hypermutation of G to A bases. Our results indicate that HIV-2, SIVSM and SIVMAC comprise a single, highly diverse group of lentiviruses which cannot be separated into distinct phylogenetic lineages according to species of origin.     

S-phase feedback control in budding yeast independent of tyrosine phosphorylation of p34cdc28.

In somatic cells, entry into mitosis depends on the completion of DNA synthesis. This dependency is established by S-phase feedback controls that arrest cell division when damaged or unreplicated DNA is present. In the fission yeast Schizosaccharomyces pombe, mutations that interfere with the phosphorylation of tyrosine 15 (Y15) of p34cdc2, the protein kinase subunit of maturation promoting factor, accelerate the entry into mitosis and abolish the ability of unreplicated DNA to arrest cells in G2. Because the tyrosine phosphorylation of p34cdc2 is conserved in S. pombe, Xenopus, chicken and human cells, the regulation of p34cdc2-Y15 phosphorylation could be a universal mechanism mediating the S-phase feedback control and regulating the initiation of mitosis. We have investigated these phenomena in the budding yeast Saccharomyces cerevisiae. We report here that the CDC28 gene product (the S. cerevisiae homologue of cdc2) is phosphorylated on the equivalent tyrosine (Y19) during S phase but that mutations that prevent tyrosine phosphorylation do not lead to premature mitosis and do not abolish feedback controls. We have therefore demonstrated a mechanism that does not involve tyrosine phosphorylation of p34 by which cells arrest their division in response to the presence of unreplicated or damaged DNA. We speculate that this mechanism may not involve the inactivation of p34 catalytic activity.     

黑曲霉胞外葡萄糖淀粉酶的纯化及特性

黑曲霉（Ａｓｐｅｒｇｉｌｌｕｓｎｉｇｅｒ７２８）的粗酶液，经硫酸铵沉淀，ＳｅｐｈａｄｅｘＧ－２５柱凝胶过滤脱盐，ＤＥＡＥ－Ｔｏｙｏｐｅａｒｌ离子交换柱层析和ＳｅｐｈａｃｒｙＳ－１００凝胶层析纯化，经ＰＡＧＥ鉴定为一条带ＳＤＳ凝胶电泳测定分子量为７００００．金属离子Ｆｅ３＋对该酶有一定的抑制作用，该酶的等电点为３．７，最适ｐＨ为４，最适温度为６０℃．Ｅ２８０１％为１５．７２，Ｋｍ值为０．１１２×１０－３ｍ．