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231.
The Wolf-Hirschhorn syndrome (WHS) is caused by a partial deletion in the short arm of chromosome 4 band 16.3 (4p16.3). A unique-sequence human DNA probe (39 kb) localized within this region has been used to search for sequence homology in the apes' equivalent chromosome 3 by FISH-technique. The WHS loci are conserved in higher primates at the expected position. Nevertheless, a control probe, which detects alphoid sequences of the pericentromeric region of humans, is diverged in chimpanzee, gorilla, and orangutan. The conservation of WHS loci and divergence of DNA alphoid sequences have further added to the controversy concerning human descent. 相似文献
232.
Genetic studies have uncovered many genes that are involved in the first steps of neuronal development inDrosophila.Less is known about the intermediate steps during which individual precursor cells follow either the neuronal pathway or the glial pathway. We report the identification of a novel bHLH gene,biparous,expressed in neuronal and glial precursors inDrosophila.Unlike most bHLH genes,biparousexpression continues to the final stages of neurogenesis in the embryo. Expression ofbiparousis not observed in end stage postmitotic neurons and precedes the expression ofrepo,a gene activated in later stages of glial differentiation. The bHLH domain is sufficiently different from previously described bHLH domains to imply a novel function. 相似文献
233.
234.
B. Eva Villaroya Luis A. Oro Fernando J. Lahoz Andrew J. Edwards Miguel A. Ciriano Pablo J. Alonso Antonio Tiripicchio Marisa Titipicchio Camellini 《Inorganica chimica acta》1996,250(1-2):241-264
The multiple coordination possibilities of 1,8-naphthyridine-2-one (HOnapy) and 5,7-dimethyl-1,8-napthyridine-2-one (HOMe2napy) ligands allow the synthesis of a variety of tri- di- and mononuclear complexes, showing fluxional behaviour and frequent exchange of the coordinated ML2 fragments. Thus, reactions of [M2(μ-OMe)2(cod)2] (cod = 1,5-cyclooctadiene) with HOnapy and HOMe2napy yield the compounds of the general formula [M(μ-OR2napy) (cod)]n (M = Ir, R = Me (1a, 1b, H (2); M = Rh, R = Me (3a, 3b). They crystallise as inconvertible yellow (a) and purple/orange (b) forms and also show a puzzling behaviour in solution. X-ray diffraction studies on both forms (3a, 3b) and spectroscopic data reveal that the yellow forms are mononuclear complexes whilst the dark-coloured crystals contain dinuclear complexes. In solution, the nuclearity of the complexes depends on the solvent. In addition both types of complexes are fluxional. The mixed-ligand complexes [M2(μ-OMe2napy)2(CO)2(cod)] M = Ir (5), Rh (6) have been isolated and characterised; they are found to be intermediates in the synthesis of the trinuclear complexes [M3(μ3-OMe2napy)2(CO)2(cod)2]+ M = Rh (8), Ir (9). Reactions of [IrCl(CO)2(NH2-p-tolyl] with the complexes [Rh(μ-OR2napy)(diolefin)]n followed by addition of a poor donor anion is a general one-pot synthesis for the hetertrinuclear complexes [Rh2Ir(μ3-OR2napy)2(CO)2(diolefin)2]+ (R=Me, DIOLEFIN = cod (10), tetrafluorobenzo-barrelene (tfbb) (11), 2,5-norbornadiene (nbd) (12); R=H, DIOLEFIN=cod (13)). This synthesis follows a stepwise mechanism from the mononuclear to the trinuclear complexes in which mixed-ligand heterodinuclear complexes are involved as intermediates of the type [(diolefin)Rh(μ-OMe2napy)2Ir(CO)2]. Heteronuclear complexes which possess the core [RhIr2]3+, such as [RhIr2(μ3-OR2napy)2(CO)2(cod)2]BF4 (R=Me (14), H (15)), result from the reaction of 1 or 2 with [Rh(CO)2Sx]+ (S = solvent). The trinuclear complexes undergo two chemically reversible one-electron oxidation processes. The chemical oxidation of 10, 14 and 9 with silver salts gives the mixed-valence trinuclear radicals [Rh2Ir(μ3-OMe2napy)2(CO)2(cod)2]2+ (16), [RhIr2(μ3-OMe2napy)2(CO)2(cod)2]2+ (17) and [Ir3(μ3-OMe2napy)2(CO)2(cod)2]2+ (18), which have been isolated as the perchlorate and tetrafluoroborate salts. The EPR spectrum of 16 indicates that the unpaired electron is essentially in an orbital delocalised on the metals. The molecular structures of the complexes 3a, 3b, 6, 10b and 16a are described. Crystals of 3a are triclinic, P-1, with a = 9.7393(2), b = 14.0148(4), c = 16.0607(4) Å, α = 88.122(3), β = 83.924(3), γ = 87.038(3)°, Z = 4; 3b crystallises in the Pna2i orthorhhombic space group, with a = 16.7541(3), B = 11.7500(8), c = 17.7508(7) Å, Z = 4; complex 6 is packed in the monoclinic space group P2i/c, a = 9.6371(1), b = 11.8054(4), c = 27.2010(9) Å, β = 90.556(4)°, Z = 4; crystals of 10b are monoclinic, P21/n, with a = 17.546(7), b = 13.232(6), c = 17.437(8) Å, β = 106.18(1)°, Z = 4; crystals of 16a are triclinic, P-1, with a = 10.318(4), b = 12.562(6), C = 19.308(8) Å, α = 92.12(8), β = 97.65(9), γ = 90.68(5)°, Z = 2. The five different structures show the coordination versatility of the OMe2napy molecule as ligand, which behaves as a N,N′-chelating (3a), bidentate N,O-donor (3b, 6), or as a tridentate N,N′,O-donor bridging ligand (10b, 16a). 相似文献
235.
The reactions of cadmium halides with the 15-membered macrocyclic crown ethers, 15-crown-5 and benzo-15-crown-5, have been carried out and six new complexes have been isolated and structurally characterized. Metal to ligand stoichiometries of 1:1, 2:1, 3:1 and 3:2 have been observed with a variety of different formulations. Examples of charge separated ion pairs ([(NH4)(benzo-15-crown-5)2]2[Cd2I6]), halogen bridged monomers, dimers or polymers ([Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2(isolated from the same reaction mixture) and [(CdCl2)2CdCl2(15-crown-5)]n), and hydrogen bonded finite chains or polymers ([(Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN and [CdI2(OH2)2(THF)]·benzo-15-crown-5) have been isolated. Three different types of 15-crown-5 coordination modes have been observed in these complexes. In-cavity coordination resulting in pentagonal bipyramidal geometries about Cd2+ was observed in [(CdCl2)2CdCl2(15-crown-5)]n, [Cd(15-crown-5)(OHMe)(μ-Br)CdBr3], and [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN, [Cd(15-crown-5)(μ-Br)2CdBr(μ-Br)]2 displays out-of-cavity coordination with one etheric donor distorted into an axial position of a distorted pentagonal bipyramid. The third coordination mode is secondary sphere coordination via hydrogen bonding which is observed for [Cd(OH2)2(15-crown-5)][CdI3(OH2)]2·2(15-crown-5)·2CH3CN. The good fit of Cd2+ within the cavity of 15-crown-5 results in shorter bonding contacts and a more narrow distribution in Cd---O values (2.273(7)-2.344(6) Å) than observed for cadmium halide complexes of 18-crown-6 (Cd---O = 2.69(1)–2.81(1) Å). 相似文献
236.
237.
Dong-Uk Kim Seung-Kiel Park Kyung-Sook Chung Myung-Un Choi Hyang-Sook Yoo 《Molecular & general genetics : MGG》1996,252(1-2):20-32
ASchizosaccharomyces pombe homolog of mammalian genes encoding G protein subunits,gpb1
+, was cloned by the polymerase chain reaction using primer pairs that correspond to sequences conserved in several G genes of other species followed by screening of genomic and cDNA libraries. Thegpb1 gene encodes 317 amino acids that show 47% homology with human G
1 and G
2 and 40% homology withSaccharomyces cerevisiae G protein. Disruption of thegpb1 gene indicated that this gene is not required for vegetative cell growth. However,gpb1-disrupted haploid cells mated and sporulated faster than wild-type cells, both in sporulation (MEA) and in complex medium (YE): when examined 23 h after transfer to sporulation medium, 35% ofgpb1-disrupted haploid pairs had undergone conjugation and sporulation, whereas only 3–5% of wild-type haploid pairs had done so. Overexpression of thegpb1 gene suppressed this facilitated conjugation and sporulation phenotype ofgpb1-disrupted cells but did not cause any obvious effect in wild-type cells. Co-disruption of one of the twoS. pombe G-subunit genes,gpa2, in thegpb1-disrupted cells did not change the accelerated conjugation and sporulation phenotype of thegpb1
– cells. However, co-disruption of theras1 gene abolished thegpb1
– phenotype. These results suggest that Gpbl is a negative regulator of conjugation and sporulation that apparently works upstream of Ras1 function inS. pombe. The possible relationship of Gpbl to two previously identified, putative G proteins ofS. pombe is discussed.A preliminary report of this work first appeared in an abstract of the Genetic Society of America, 1993 Yeast Genetics and Molecular Biology Meeting, p. 92 and was presented at the American Association of Cancer special meeting on Cell Signalling and Cancer Treatment, 1993 相似文献
238.
Airborne particles and ammonia were monitored in horse stalls managed under four conditions. Two ventilation rates, high (27 air changes per h) and low (5 air changes per h) and two bedding types, paper and straw, were employed. At both ventilation rates, the number of airborne particles generated while the stalls were mucked out was higher with straw than with paper. Particles were more efficiently cleared at the higher ventilation rate in both the straw and paper stalls. Ammonia measurements reflected an accumulation over time. In the stalls with low ventilation, ammonia levels were significantly higher than in those stalls with high ventilation regardless of bedding type. Management decisions and their relationships to respiratory disorders are discussed. 相似文献
239.
Aspects of the reproductive biology of the concha wrasse, Nelabrichthys ornatus, at Tristan da Cunha 总被引:1,自引:0,他引:1
Synopsis The reproductive biology of the concha wrasse, Nelabrichthys ornatus, at Tristan da Cunha in the South Atlantic Ocean is described. Histological evidence shows that the species is a monandric protogynous hermaphrodite. N. ornatus displays full permanent sexual dichromatism with all males occurring in the upper size classes of the population. Size specific habitat preference is described. Aspects of the mating system of the species resemble a lek although the possibility of mating site selection by females is not discounted. Spawning groups have a sex ratio of between 4 and 7 females per male. 相似文献
240.
Summary A heterologous gene from bloodsucking leech for anticoagulant, hirudin, has been expressed in the methylotrophic yeast Hansenula polymorpha. The addition of 1%(v/v) soybean oil to the medium as a stabilizer enhanced the expression of the hirudin gene in H. polymorpha with MOX promoter. The production of hirudin in the medium with soybean oil was 320mg/L in a 5L fermenter. 相似文献