The nature of the stable noncovalent dimers of band 3 protein from erythrocyte membranes in solutions of Triton X-100

Stable noncovalent dimers of band 3 protein from human erythrocyte membranes, in which state the protein is thought to exist after solubilization by the nonionic detergent Triton X-100, do not occur when purified batches of the detergent are used. Instead, the protein is in a monomer/dimer/tetramer association equilibrium. The stable dimers do appear, however, when the detergent has been 'aged'. They thus seem to be artifacts.     

Theoretical conformational analysis of phospholipids II. Role of hydration in the gel to liquid crystal transition of phospholipids

To obtain a satisfactory agreement between computed transition temperatures and those determined experimentally, we introduce explicitly water molecules which hydrate the polar headgroup of dipalmitoylphosphatidylethanolamine molecules. The calculated free energy curves as a function of the intermolecular interchain distance and the degree of hydration of the polar groups permit the determination of the transition of the phospholipid system from the gel to the liquid crystalline phase. The detailed structure of the hydration shell is defined using the supermolecular approach.     

Germ cell nucleosomes contain remodeled core protein complex

Electrophoretic analysis of the nucleosomal histones from MN1 and MN2 subpopulations of the seminiferous tubules in gels containing either 6.25 or 2.5 M urea revealed the presence of testis specific histone H2S, H1 and protein ‘A’ in addition to the somatic histones in the core protein complex. Size analysis indicated the presence of a 150–160 bp DNA segment in the MNI subpopulation, whereas, an approx 180 bp DNA fragment was present in the MN2 subpopulation of both liver and tubule nucleosomes. These data suggest an extensive remodeling of the nucleosomal core protein complex during mammalian spermatogenesis.     

Der Feinbau der sog. Kugelhaare der Fadenkanker (Opiliones,Nemastomatidae)

Zusammenfassung Der Hohlraum des Kugelhaares von Nemastoma bildet im basalen Teil Ausbuchtungen mit tubulären Strukturen, die mit 40–50 von proximal nach distal ziehenden Kanälen in Verbindung stehen.Nahe der Haarspitze befindet sich ein hohler Schirm mit zahlreichen Chaetoiden. Dicht unter ihm öffnen sich die Kanäle nach außen, und zwar derartig, daß ihr zentrad gelegener Teil der Wand den Schirmstiel bildet, während sich ihr peripherwärts gelegener Wandteil in einzelne Streben aufgliedert. Diese bilden nach Erreichen des Schirmbodens zwischen sich und dem Schirmstiel einen großen Hohlraum, der von einem klebrigen Sekret angefüllt und, zusammen mit dem Schirm, auch umhüllt wird.

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The fine structure of spezialized setae on the pedipalpi of nemastoma (Opiliones, Nemastomatidae)

Summary The cavity of the seta on the pedipalpi of Nemastoma shows protrusions with tubular structures, which are connected with 40–50 channels proceeding from proximal towards distal.Close by the tip of the seta there is a hollow umbrella with numerous secondary chetae. Bight underneath, each channel is widened in a way that the central part of the wall builds the stalk of the umbrella, whereas the more peripheral part of the wall is split in single struts. Both struts fused with the umbrella and its stalk form a large cavity. This cavity is filled with a viscid droplet and enveloped as well together with the umbrella. — The possible meaning of these structures is discussed.

Frl. A. Hennig bin ich für ihre gewissenhafte technische Mitarbeit sehr zu Dank verpflichtet.     

Melanogenesis in amphibians

Summary The pigmented epithelium of Rana pipiens tadpole eyes normally develops at least two types of melanosomes: (1) an elongated melanin granule of relatively homogeneous electron density, and (2) a complex melanosome which has an outer electrondense area and one or more less dense cores. Evidence indicates that complex melanosomes are formed by new melanin enclosing preexisting melanosomes. An organized fibrillar premelanosome is demonstrated with the aid of the antimelanogenic compound phenylthiourea (PTU). These premelanosomes are the developing forms of the elongated melanosomes. There is evidence that the premelanosomes originate in the smooth endoplasmic reticulum. Phenylthiourea blocks melanin synthesis in the premelanosomes; however, removal of the PTU allows pigment deposition. This finding of an organized, fibrillar premelanosome in an amphibian marks the lowest phylogenetic group in which these organelles have been described.An Oak Ridge Graduate Fellow from Catholic University of America, Washington, D.C., under appointment from Oak Ridge Associated Universities.The MAN Program is supported by the National Cancer Institute, the National Institute of General Medical Sciences, the National Institute of Allergy and Infectious Diseases, and the U.S. Atomic Energy Commission.Oak Ridge National Laboratory is operated by Union Carbide Corporation Nuclear Division for the U.S. Atomic Energy Commission.     

A note on sequence-dependence of DNA structure

A circular dichroism study was conducted on the solution structure of several different oligonucleotides, whose X-ray structures have been solved. It is suggested that in aqueous solution the oligonucleotides can form structures that maintain geometrical elements which are typical of B-DNA, A-DNA, and their intermediate forms. It is shown that 5'GGATGGGAG:5'CTCCCATCC, which forms an A-DNA helix in the crystal state (McCall et al. 1986), in aqueous solution maintains an A-DNA like structure at temperatures below 10 degrees C. At temperatures between 10 degrees C and 25 degrees C it shows a tendency to form an intermediate structure between A-DNA and B-DNA. Also, it is shown that TFE does not cause a transition from B-DNA to A-DNA helix in short DNA fragments, but instead disrupts the helix.     

用定点突变技术研究转录终止——rpoBC操纵子上~tL7茎环结构的作用研究

 E.coli RNA聚合酶ββ'亚单位编码的基因rpoBC与核糖核蛋白基因rplJL共同构成rpoBC操纵子。rpl-rpo间区转录终止信号~tL7的转录产物RNA有两组富含C-G的反向对称结构及一串寡聚U;反向对称区可形成1:2和3:4茎环或单一5:6茎环。 用M13mp11噬菌体插入~tL7的112bp片段重组M13mp11-490,在此基础上用定点突变技术建立~tL7的七核苷酸缺失突变体,从而破坏1:2茎环,建成M13mp11-85。 分别把原型~tL7及缺失型~tL7~v克隆到表达质粒pHR24中,构建成pHR37(P_ftsQ~tL7-galk)及pHR24-9(p_ftsQ-~tL7~v-galk)。测定galk基因产物半乳糖激酶活性,推算转录的终止效率。结果表明:~tL7终止效率为50％,~tL7~v为20％。说明仅有3:4茎环及寡聚U,即具终止作用; 1:2茎环通过某种方式加强3:4茎环从而提高终止效率。     

Recolonisation and recruitment of fishes to intertidal rockpools at Wellington, New Zealand

Synopsis A study of recolonisation of rockpools by intertidal fishes on the Wellington south coast, New Zealand, found the assemblage to be resilient and seasonally stable. A total of 26 species from nine families were recorded, dominated by the Tripterygiidae (triplefins) and Gobiesocidae (clingfishes). A pattern of alternating species dominance occurred, with the triplefinsBellapiscis medius andForsterygion lapillum being numerically dominant in summer, but becoming less common in winter and replaced as dominants by the clingfishesTrachelochismus pinnulatus andGastroscyphus hectoris. Juvenile recruits of eleven species occurred in the samples from spring to early summer, however only the aforementioned four species recruit to the intertidal zone in large numbers. The speed of rockpool recolonisation by fishes after extractive sampling is seasonally dependent, being quicker in the summer than winter. In general, recolonisation takes at least one month, but probably fewer than three. While stochastic factors influence assemblage composition in the short term, overall regulation of the fish assemblage of rockpools appears to be primarily deterministic, resulting in an essentially predictable taxonomic structure.