A mutation in the tRNA(Leu)(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies

Mitochondrial encephalomyopathies are usually divided into three distinct clinical subgroups: (1) mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS); (2) myoclonus epilepsy associated with ragged-red fibres (MERRF); and (3) chronic progressive external ophthalmoplegia (CPEO) including Kearns-Sayre syndrome. Large deletions of human mitochondrial DNA and a transition mutation at the mitochondrial transfer RNALys gene give rise to CPEO including Kearns-Sayre syndrome and MERRF, respectively. Here we report an A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNA(Leu)(UUR) that is specific to patients with MELAS. Because this mutation creates an ApaI restriction site, we could perform a simple molecular diagnostic test for the disease. The mutation was present in 26 out of 31 independent MELAS patients and 1 out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested. Southern blot analysis confirmed that the mutant DNA always coexists with the wild-type DNA (heteroplasmy).     

ANLL中转录因子GATA—2基因点突变

了解转录因子ＧＡＴＡ－２基因在ＡＮＬＬ中的表达和突变情况,方法：采用ＲＴ－ＰＣＲ检测８５例ＡＮＬＬ病人外周血单个核细胞中ＧＡＴＡ－２基因的表达情况,ＰＣＲ产物进一步经单链构象多态性（ＳＳＣＰ）分析以了解基因突变情况。结果：绝大多数ＡＮＬＬ都表达了ＧＡＴＡ－２基因（８９．４％）,ＳＳＣＰ分析发现一例Ｍ２型的ＰＣＲ产物出现异常迁移带,核苷序列分析显示在ＧＡＴＡ－２基因第８９２位的核苷酸出现点突变,即第     

Trembler mouse carries a point mutation in a myelin gene.

The autosomal dominant trembler mutation (Tr), maps to mouse chromosome 11 (ref. 2) and manifests as a Schwann-cell defect characterized by severe hypomyelination and continuing Schwann-cell proliferation throughout life. Affected animals move clumsily and develop tremor and transient seizures at a young age. We have recently described a potentially growth-regulating myelin protein, peripheral myelin protein-22 (PMP-22; refs 7, 8), which is expressed by Schwann cells and found in peripheral myelin. We now report the assignment of the gene for PMP-22 to mouse chromosome 11. Cloning and sequencing of PMP-22 complementary DNAs from inbred Tr mice reveals a point mutation that substitutes an aspartic acid residue for a glycine in a putative membrane-associated domain of the PMP-22 protein. Our results identify the PMP-22 gene as a likely candidate for the mouse trembler locus and will encourage the search for mutations in the corresponding human gene in pedigrees with hypertrophic neuropathies such as Charcot-Marie-Tooth and Dejerine-Sottas diseases (hereditary motor and sensory neuropathies I and III).     

Haemophilia B caused by a point mutation in a donor splice junction of the human factor IX gene

Haemophilia B (Christmas disease) is an inherited, recessive, sex-linked, haemorrhagic condition caused by a defect in the intrinsic clotting factor IX. This disease occurs in males at a frequency of approximately 1 in 30,000. Patients differ in the severity of their clinical symptoms, and variation in the clotting activity and in the concentration of factor IX antigen in their plasma has been demonstrated. There is probably heterogeneity in the molecular defects of the factor IX gene causing the disease. Here we study a severely affected, antigen-negative patient, and show that the only significant sequence difference from the normal factor IX gene is a point mutation changing the obligatory GT to a TT within the donor splice junction of exon f. We infer that this change is the cause of the disease in this individual. In addition, we have used oligodeoxynucleotide probes specific for this mutation to demonstrate the feasibility of carrier detection and prenatal diagnosis for relatives of the patient.     

Uncoupling of the recombination and topoisomerase activities of the gamma delta resolvase by a mutation at the crossover point

In several well-characterized site-specific recombination systems it has been shown that, for efficient recombination, the two recombining sites must have identical DNA sequences across the region between the staggered points of exchange. The precise DNA sequence of this overlap region, however, appears to be of little importance (with the exception of one position in the loxP site of bacteriophage P1 (ref. 6]. In this report we characterize a mutant recombination site for the site-specific recombination enzyme gamma delta resolvase (encoded by the gamma delta transposon), in which the dinucleotide at the crossover point is changed from AT to CT. Our results indicate that identity of the two overlap regions is not sufficient for recombination. Although resolvase binds normally to the mutant site and induces the structural deformation characteristic of the wild-type recombination site, catalysis at the crossover point (cutting and rejoining of DNA strands) is effectively limited to just one of the two strands, allowing resolvase to act as a topoisomerase but not as a recombinational enzyme.     

A mutation in the conserved helix termination peptide of keratin 5 in hereditary skin blistering.

In the hereditary blistering condition epidermolysis bullosa simplex, the skin blisters on trauma following rupture of epidermal basal cells. Clinical variations range from severely incapacitating, especially in early childhood, to mild forms that may not even present clinically. Dowling-Meara epidermolysis bullosa simplex is characterized by clusters of epidermal blisters and keratin clumping in the cytoplasm; recent reports describe potentially causal mutations in keratin 14 (refs 2, 3). Here we describe a 'complementary' mutation at the other end of the other keratin expressed by these cells (K5, coexpressed with K14), a change from a Glu to a Gly in the helix termination peptide, detected by altered antibody binding and confirmed by sequencing using the polymerase chain reaction. The two conserved helix boundary peptides are predicted to be essential for filament assembly, and the requirement for two complementary (type I and type II) keratins is absolute. Epidermolysis bullosa simplex diseases demonstrate the function of the keratin cytoskeleton in resisting compaction stresses which otherwise lead to cell lysis.     

Altered chloride ion channel kinetics associated with the delta F508 cystic fibrosis mutation.

Cystic fibrosis is associated with a defect in epithelial chloride ion transport which is caused by mutations in a membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator). Heterologous expression of CFTR produces cyclicAMP-sensitive Cl(-)-channel activity. Deletion of phenylalanine at amino-acid position 508 in CFTR (delta F508 CFTR) is the most common mutation in cystic fibrosis. It has been proposed that this mutation prevents glycoprotein maturation and its transport to its normal cellular location. We have expressed both CFTR and delta F508 CFTR in Vero cells using recombinant vaccinia virus. Although far less delta F508 CFTR reached the plasma membrane than normal CFTR, sufficient delta F508 CFTR was expressed at the plasma membrane to permit functional analysis. delta F508 CFTR expression induced a reduced activity of the cAMP-activated Cl- channel, with conductance, anion selectivity and open-time kinetics similar to those of CFTR, but with much greater closed times, resulting in a large decrease of open probability. The delta F508 mutation thus seems to have two major consequences, an abnormal translocation of the CFTR protein which limits membrane insertion, and an abnormal function in mediating Cl- transport.     

Inhibition of RNA cleavage but not polyadenylation by a point mutation in mRNA 3' consensus sequence AAUAAA

A single U leads to G transversion in the 3' consensus sequence AAUAAA of the adenovirus early region 1A gene was constructed and the effect of this mutation on processing of the 3' end of the nuclear early region 1A RNAs was analysed. The results demonstrate that the intact AAUAAA is not required for RNA polyadenylation but is required for the cleavage step preceding polyadenylation to occur efficiently.     

引入随机子群蚁群算法的JSP仿真与研究

针对标准蚁群算法易于出现早熟停滞等缺陷,在原有算法基础上引入一定比例的随机蚁群.在优化过程中随机蚁群以一定概率做随机搜索,以扩大了解的搜索空间;在信息素更新策略上,为了兼顾当代和历代的搜索成果,采取了信息素混合更新策略,同时增强随机子群的最佳路径信息及剩余全部蚁群路径信息,有效抑制了收敛过程中的早熟停滞现象,提高了算法收敛速度.通过典型作业车间调度问题(JSP)实例进行了仿真实验,表明该算法不仅能够克服早熟现象,而且能够加快收敛速度.     

线粒体DNA突变与母系遗传病

近几年来,线粒体DNA(mtDNA）突变与人类疾病及母系遗传病的关系愈来愈受到人们的关注。从分子水平上探讨mtDNA突变的发生情况及mtDNA突变所引起的遗传病的表达及传递方式,有助于揭开线粒体遗传病的本质,最终为人类防治线粒体遗传病提供理论基础。     

A stop-codon mutation in the BRI gene associated with familial British dementia

Familial British dementia (FBD), previously designated familial cerebral amyloid angiopathy-British type, is an autosomal dominant disorder of undetermined origin characterized by progressive dementia, spasticity, and cerebellar ataxia, with onset at around the fifth decade of life. Cerebral amyloid angiopathy, non-neuritic and perivascular plaques and neurofibrillary tangles are the predominant pathological lesions. Here we report the identification of a unique 4K protein subunit named ABri from isolated amyloid fibrils. This highly insoluble peptide is a fragment of a putative type-II single-spanning transmembrane precursor that is encoded by a novel gene, BRI, located on chromosome 13. A single base substitution at the stop codon of this gene generates a longer open reading frame, resulting in a larger, 277-residue precursor. Release of the 34 carboxy-terminal amino acids from the mutated precursor generates the ABri amyloid subunit. The mutation creates a cutting site for the restriction enzyme XbaI, which is useful for detecting asymptomatic carriers. Antibodies against the amyloid or homologous synthetic peptides recognize both parenchymal and vascular lesions in FBD patients. A point mutation at the stop codon of BRI therefore results in the generation of the ABri peptide, which is deposited as amyloid fibrils causing neuronal disfunction and dementia.     

Discovery of mitochondrial chimeric-gene associated with cytoplasmic male sterility of HL-rice

The mitochondrial genome libraries of HL-type sterile line (A) and maintainer line (B) have been constructed. Mitochondrial gene, atp6 , was used to screen libraries, due to the different Southern and Northern blot results between sterile and maintainer line. Sequencing analysis of positive clones proved that there were two copies of atp6 gene in sterile line and only one in maintainer line. One copy of atp6in sterile line was same to that in maintainer line; the other showed different flanking sequence from the 49th nucleotide downstream of the termination codon of atp6 gene. A new chimeric gene, orfH79 , was found in the region. orfH79 had homology to mitochondrial gene coxⅡ and orfH79, and was special to HL-sterile cytoplasm.     

A point mutation of the rhodopsin gene in one form of retinitis pigmentosa

The gene for autosomal dominant retinitis pigmentosa in a large pedigree of Irish origin has recently been found to be linked to an anonymous polymorphic sequence, D3S47 (C17), from the long arm of chromosome 3. As the gene coding for rhodopsin is also assigned to the long arm of chromosome 3 and is expressed in rod photoreceptors that are affected early in this blinding disease, we searched for a mutation of the rhodopsin gene in patients with autosomal dominant retinitis pigmentosa. We found a C----A transversion in codon 23 (corresponding to a proline----histidine substitution) in 17 of 148 unrelated patients and not in any of 102 unaffected individuals. This result, coupled with the fact that the proline normally present at position 23 is highly conserved among the opsins and related G-protein receptors, indicates that this mutation could be the cause of one form of autosomal dominant retinitis pigmentosa.     

A point mutation in the neu oncogene mimics ligand induction of receptor aggregation

The rat neu gene, which encodes a protein closely related to the epidermal growth factor receptor, is a proto-oncogene that can be converted into an oncogene by a point mutation. Both genes encode proteins with a relative molecular mass of 185,000 but the question of why the neu gene product, p185neu, is oncogenic, whereas the product of c-neu, p185c-neu, is not, remains unanswered. The proteins have several features common to the family of tyrosine kinase growth-factor receptors, including cysteine-rich external domains, a hydrophobic transmembrane region and a cytoplasmic tyrosine kinase domain. The oncogenic p185neu differs from p185c-neu by an amino-acid substitution in the transmembrane region of the glycoprotein: this replacement of valine by glutamic acid at position 664 induces increased intrinsic tyrosine kinase activity which is associated with transformation. Many glycoproteins with charged amino acids in the transmembrane region exist as multimeric complexes at the plasma membrane. We have therefore investigated the association state of both products of the neu gene and show that the oncoprotein p185neu is organized at the plasma membrane primarily in an aggregated form, but that p185c-neu is not. Induction of an aggregated state may mimic aspects of ligand-induced receptor aggregation resulting in enzymatic activation that leads to cellular transformation.