Biphasic mineral nutrition of the submersed aquatic macrophyte Potamogeton pectinatus L.

The mineral nutrition of a clone of the submersed aquatic macrophyte Potamogeton pectinatus L. was examined in relation to the ability of the roots to mobilize N, P, K, S, Ca, Mg, dissolved inorganic C and micronutrients to the shoots from a constant small volume of sediment in the absence of one or more of these nutrients in the water phase. Survival, biomass production and shoot nutrient concentration values were measured after 35 days of growth under controlled conditions. Flower production and shoot morphology were also noted.The roots of P. pectinatus were capable of mobilizing sufficient P, N, S, K and micronutrients from the sediment to the shoots to meet normal growth requirements. In the absence of K from the water phase, Na replaced it, but the vigor of the plants suffered somewhat by the substitution. The roots were not capable of mobilizing sufficient Mg, Ca, or dissolved inorganic C from the sediment to the shoots to meet normal growth requirements. Survival and normal growth occurred with a minimum of 2 ppm Ca, 10 ppm Mg, and 0.5 meq HCO₃^? in the water phase. Water-phase Ca was necessary to prevent the toxicity of other cations such as Mg when present in the water phase.A seasonal periodicity in biomass production occurred under standardized environmental conditions, suggesting an internal regulation independent of obvious external signals.     

The effect of temperature on the self-association of S5 and on the association of S5 with S8 as determined by sedimentation equilibrium

Solutions of proteins S5 and S8 from the Escherichia coli 30 S ribosomal subunit have been examined by sedimentation equilibrium methods as a function of temperature for their behavior in solution as isolated components and in mixtures. The standard enthalpy and entropy at 4 °C for the isodesmic self-association of S5 were determined from a study over the temperature range of 3 to 33 °C to be 0.1 ± 0.9 kcal/mol and 18 ± 3 cal/(mol × deg), respectively. The protein S8 remained monomeric over the same range of temperature. The standard enthalpy and entropy at 4 °C for the association of S5 and S8 were determined on mixtures from a study over the temperature range of 3 to 27 °C to be ?0.4 ± 1.6 kcal/mol and 20 ± 6 cal/(mol × deg), respectively. Based on these values and the previously determined standard Gibbs free energies (S. H. Tindall and K. C. Aune, 1981, Biochemistry20, 4861–4866), the driving force for the self-association of S5 and the association of S5 with S8 could be interpreted as being derived from the expulsion of water upon ion pair formation at the interaction sites.     

The OR control system of bacteriophage lambda. A physical-chemical model for gene regulation

A quantitative model has been developed for processes in the bacteriophage lambda that control the switchover from lysogenic to lytic modes of growth. These processes include the interactions of cI repressor and cro proteins at the three DNA sites of the right operator, OR, the binding of RNA polymerase at promoters PR and PRM, the synthesis of cI repressor and cro proteins, and the degradative action of recA during induction of lysis. The model is comprised of two major physical-chemical components: a statistical thermodynamic theory for relative probabilities of the various molecular configurations of the control system; and a kinetic model for the coupling of these probabilities to functional events, including synthesis of regulatory proteins cI and cro. Using independently evaluated interaction constants and rate parameters, the model was found capable of predicting essential physiological characteristics of the system over an extended time. Sufficiency of the model to predict known physiological properties lends credence to the physical-chemical assumptions used in its construction. Several major physiological characteristics were found to arise as "system properties" through the non-linear, time-dependent, feedback-modulated combinations of molecular interactions prescribed by the model. These include: maintenance of the lysogenic state in the absence of recA-mediated cI repressor degradation; induction of lysis and the phenomenon of subinduction; and autogenous negative control of cro. We have used the model to determine the roles, within the composite system, of several key molecular processes previously characterized by studies in vitro. These include: co-operativity in cI repressor binding to DNA; interactions between repressors and RNA polymerase (positive control); and the monomer-dimer association of cI repressor molecules. A major role of cI repressor co-operativity is found to be that of guaranteeing stability of the lysogenic state against minor changes in cI repressor levels within the cell. The role of positive control seems to be that of providing for a peaked, rather than monotonic, dependence of PRM activity on cI repressor level, while permitting PR activity to be a step function. The model correlates an immense body of studies in vivo and in vitro, and it makes testable predictions about molecular phenomena as well as physiological characteristics of bacteriophage lambda. The approach developed in this study can be extended to include more features of the lambda system and to treat other systems of gene regulation.     

Genes and pseudogenes for human U2 RNA: Implications for the mechanism of pseudogene formation

Three loci, designated U2/4, U2/6 and U2/7, which contain sequences related to human U2 RNA, have been studied. The U2/6 locus contains a tandem array of bona fide U2 genes. U2/4 and U2/7, in contrast, contain pseudogenes whose sequences deviate significantly from that of mammalian U2 RNA. The two pseudogenes appear to have been created by different mechanisms. The sequences that flank the pseudogene in the U2/4 locus lack homology to the corresponding sequences in functional human U2 genes, except for 10 base-pairs immediately following the 3′ end. The conserved 3′-flanking segment is homologous to those nucleotides that are present in a U2 RNA precursor. No direct repeats flank the pseudogene in the U2/4 locus. The observations thus suggest that a complementary DNA copy of the U2 RNA precursor was inserted into a blunt-ended chromosomal break to generate the U2/4 locus.The U2/7 locus, in contrast, revealed flanking sequence homology when compared to functional U2 genes, both on the 5′ and 3′ sides of the pseudogene. The homology was interrupted on both sides by repetitive sequences belonging to the Alu family. On the 5′ side the homology continues beyond the Alu repeats whereas on the 3′ side it ends precisely at the Alu repeat. This Alu repeat is inserted in a region where a homocopolymeric region of alternating C and T residues is located in functional U2 loci. The observed organization of the U2/7 locus suggests that a previously functional U2 locus was invaded by Alu repeats and subsequently accumulated base substitutions to become a pseudogene.     

The synthesis of 8-(6-aminohexyl)-amino-GMP and its applications as a general ligand in affinity chromatography.

The steady-state kinetic behaviors of the five rabbit adrenal norepinephrine N-methyl transferase isozymes have been compared with particular reference to substrate inhibition patterns. Four distinct substrate inhibition patterns were observed. The E-1 isozyme was not subject to inhibition by either substrate, while the E-2 isozyme was inhibited by both substrates. The E-3 and E-4 isozymes were inhibited by norepinephrine only, while E-5 is inhibited only by S-adenosylmethionine. The substrate inhibition constants were sufficiently small in relation to the Michaelis constants to make substrate inhibition an important factor in regulation of activities of the isozymes.     

Metal ions in biological systems. vol. XVIII. Circulation of metals in the environment : Edited by Helmut Sigel,Marcel Dekker,New York and Basle, 1984, 397 pp.

The solvent, pressure and temperature dependencies of the lowest energy metal to ligand charge transfer absorption bands were studied for a series of complexes of the type Mo(CO)₄(N$\text{N}$), where N$\text{N}$ = 2,2′-bipyridine, 1,10-phenanthroline and biacetylbis(phenylimine). Throughout the series of complexes the absorption bands shift to shorter wavelength in more polar solvents or on increasing the pressure in a particular solvent, but to longer wavelengths on increasing temperature. These main tendencies can be accounted for in terms of solvent polarity and its dependence on pressure and temperature.     

Biosynthesis of monoterpenes: hydrolysis of bornyl pyrophosphate, an essential step in camphor biosynthesis, and hydrolysis of geranyl pyrophosphate, the acyclic precursor of camphor, by enzymes from sage (Salvia officinalis).

Soluble enzyme preparations from sage (Salvia officinalis) leaves catalyze the hydrolysis of (+)-bornyl pyrophosphate to (+)-borneol, which is an essential step in the biosynthesis of the cyclic monoterpene (+)-camphor [(1R,4R)-bornan-2-one] in this tissue. Chromatography of the preparation on Sephadex G-150 allowed the separation of two regions of bornyl pyrophosphate hydrolase activity. One region was further separated into a pyrophosphate hydrolase and a monophosphate hydrolase by chromatography on hydroxylapatite, but the other contained pyrophosphate and monophosphate hydrolase activities which were inseparable by this or any other chromatographic technique tested. Each phosphatase and pyrophosphatase activity was characterized with respect to molecular weight, pH optimum, response to inhibitors, K_m for bornyl phosphate or bornyl pyrophosphate, and substrate specificity, and each activity was distinctly different with regard to these properties. One pyrophosphatase activity was specific for pyrophosphate esters of sterically hindered monoterpenols such as bornyl pyrophosphate. The other preferred pyrophosphate esters of primary allylic alcohols such as geranyl pyrophosphate and neryl pyrophosphate, which are precursors of cyclic monoterpenes, and it hydrolyzed geranyl pyrophosphate at faster rates than neryl pyrophosphate. The monophosphate hydrolase activities were similar in substrate specificity, showing a preference for phosphate esters of primary allylic alcohols. The terpenyl pyrophosphate hydrolase exhibiting specificity for bornyl pyrophosphate may be involved in camphor biosynthesis in vivo, while the terpenyl pyrophosphate hydrolase more specific for geranyl pyrophosphate was shown to be a source of potential interference in studies on monoterpene cyclization processes.     

A model chromatin assembly system. Factors affecting nucleosome spacing

Poly[d(A-T)].poly[d(A-T)], when reconstituted with chicken erythrocyte core histones and subsequently incubated with sufficient histone H5 in a solution containing polyglutamic acid, forms structures resembling chromatin. H5 induces nucleosome alignment in about two hours at physiological ionic strength and 37 degrees C. The nucleosome spacing and apparent linker heterogeneity in the assembled nucleoprotein are very similar to those in chicken erythrocyte chromatin. Also, condensed chromatin-like fibers on the polynucleotide can be visualized. The binding of one mole of H5 per mole of core octamer is necessary to generate the physiological nucleosome spacing, which remains constant with the addition of more H5. The nucleosome repeat length is not a function of the core histone to poly[d(A-T)] ratio for values lower than the physiological ratio. With increasing ratios, in excess of the physiological value, nucleosome spacing first becomes non-uniform, and then takes on the close packing limit of approximately 165 base-pairs. In addition to eliminating possible base sequence effects on nucleosome positioning, poly[d(A-T)] allows nucleosomes to slide more readily than does DNA, thereby facilitating alignment. Evidence is presented that polyglutamic acid facilitates the nucleosome spacing activity of histone H5, primarily by keeping the nucleoprotein soluble. This model system should be useful for understanding how different repeat lengths arise in chromatin.     

Chromatin structure of the potential Z-forming sequence (dT-dG)n X (dC-dA)n. Evidence for an "alternating-B" conformation

The sequence (dT-dG)n X (dC-dA)n is the most abundant purine-pyrimidine dinucleotide repeat in eukaryotic genomes. This sequence and certain others that contain alternating purine-pyrimidine residues have been shown to adopt the left-handed, Z-DNA conformation in vitro when subjected to negative torsional stress or elevated ionic strengths. We have asked whether (dT-dG)n X (dC-dA)n tracts exist in topologically constrained Z-form structures in vivo by examining the chromatin organization of these sequences in cultured mouse cell nuclei. We find that these elements are quantitatively packaged into typical core particles which are embedded in canonical polynucleosomal arrays. In addition, these sequences neither flank nor reside within regions of chromatin that are preferentially sensitive to S1 nuclease. These characteristics suggest that these tracts do not exist predominantly in the Z-form in vivo. Furthermore, employing techniques that permit prominent hybridization to DNA fragments as short as 18 bases, we provide evidence that in vivo, most (dT-dG)n X (dC-dA)n elements instead adopt an "alternating-B" conformation on the nucleosomal surface.     

Group-directed modification of bacteriorhodopsin by arylisothiocyanates. Labeling, identification of the binding site and topology

Group-directed hydrophobic modification of membrane-integrated protein segments by arylisothiocyanates is applied to bacteriorhodopsin. Labeling of purple membrane with phenylisothiocyanate and 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate results in covalent modification of a unique lysine epsilon-amino group of bacteriorhodopsin. Lysine residue 41, located in the amino-terminal chymotryptic fragment, has been identified as the arylisothiocyanate binding site by established sequencing techniques. The phenylisothiocyanate binding site is not accessible for the aqueously soluble analog p-sulfophenylisothiocyanate. Furthermore, the acid-induced bathochromic shift of the bound chromophore reagent is not observed following acidification of 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate-labeled purple membrane. The modification thus occurs in the hydrophobic membrane domain, providing further evidence for intramembraneous disposition of the modified protein segment. Light-induced proton translocation is preserved in reconstituted vesicles containing either phenylisothiocyanate-modified or 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate-modified bacteriorhodopsin.     

Processing of bacteriophage T4 tRNAs. The role of RNAase III

In order to assess the contribution of the processing enzyme RNAase III to the maturation of bacteriophage T4 transfer RNA, RNAase III⁺ and RNAase III^? strains were infected with T4 and the tRNAs produced were analyzed. Infection of the RNAase III⁺ strains of Escherichia coli with T4Δ27, a deletion strain missing seven of the ten genes in the T4 tRNA cluster, results in the appearance of a transient 10.1 S RNA molecule as well as the three stable RNAs encoded by T4Δ27, species 1, rRNA^Leu and tRNA^Gln. Infection of an RNAase III^? strain results in the appearance of a larger, transient RNA molecule, 10.5 S, and a severe reduction in the accumulation of tRNA^Gln. The 10.5 S RNA is similar to 10.1 S RNA but contains extra nucleotides (about 50) at the 5′ end. (10.1 S contains all the three final molecules plus about 70 extra nucleotides at the 3′ end.) Both 10.5 S and 10.1 S RNAs can be processed in vitro into the three final molecules. When 10.1 S is the substrate, the three final molecules are obtained whether extracts of RNAase III⁺ or RNAase III^? cells are used. However, when 10.5 S is the substrate RNAase III⁺ extracts bring out normal maturation, while using RNAase III^? extracts the level of tRNA^Gln is severely reduced. When 10.5 S is used with RNAase III⁺ extracts maturation proceeds via 10.1 S RNA, while when RNAase III^? extracts were used 10.1 S is not detected. The 10.5 S RNA can be converted to 10.1 S RNA by RNAase III in a reaction which produces only two fragments. The sequence at the 5′ end of the 10.5 S suggests a secondary structure in which the RNAase III cleavage site is in a stem. These experiments show that the endonucleolytic RNA processing enzyme RNAase III is required for processing at the 5′ end of the T4 tRNA cluster where it introduces a cleavage six nucleotides proximal to the first tRNA, tRNA^Gln, in the cluster.     

Synthesis and accumulation of an extremely stable high-energy phosphate compound by muscle, heart, and brain of animals fed the creatine analog, 1-carboxyethyl-2-iminoimidazolidine (homocyclocreatine)

A new creatine analog, 1-carboxyethyl-2-iminoimidazolidine (homocyclocreatine), has been synthesized and compared with other synthetic analogs of creatine as a substrate for creatine kinase under both in vitro and in vivo conditions. Reactivity with rabbit muscle creatine kinase at 2 mM and pH 7.0 occurred in the order: creatine greater than cyclocreatine (1-carboxymethyl-2-iminoimidazolidine) greater than N-ethylguanidinoacetate greater than N-propylguanidinoacetate greater than guanidinoacetate greater than N-methyl-3-guanidinopropionate greater than 3-guanidinopropionate greater than homocyclocreatine. Homocyclocreatine was 10,000-fold less active than creatine. In the reverse direction at 0.2 mM and pH 7.0: creatine-P greater than N-ethylguanidinoacetate-P greater than cyclocreatine-P much greater than homocyclocreatine-P. Homocyclocreatine-P was 200,000-fold less active than creatine-P. The phosphoryl group transfer potential of homocyclocreatine-P was estimated to be 2 kcal/mol lower than that of creatine-P. Chicks fed 5% homocyclocreatine for 16 days synthesized and accumulated homocyclocreatine-P in breast muscle (32 mumol/g wet wt), leg muscle (24 mumol/g), heart (7 mumol/g), intestine (8.5 mumol/g), and brain (2.4 mumol/g). During ischemia homocyclocreatine-P was utilized by muscle much more slowly for the regeneration of ATP than was creatine-P or cyclocreatine-P. Our results suggest that in tissues of homocyclocreatine-fed animals subjected to a sudden large increase in work load or to ischemia, the residual creatine-P system would rapidly equilibrate with the adenylate system at the new lower cytosolic phosphorylation potential, whereas in the same cytosol the (homocyclocreatine-P)/(homocyclocreatine) ratio would exhibit a hysteresis or memory effect and reflect for a considerable period of time the earlier higher (ATP)/(free ADP) ratio rather than the actual lower (ATP)/(free ADP) ratio.     

The geometry of the thioester group and its implications for the chemistry of acyl coenzyme A

L-929 cell surface membranes were incubated with S-adenosyl-l-[methyl-³H]-methionine and found to contain phosphatidylethanolamine: S-adenosylmethionine N-methyltransferase (phosphatidylethanolamine N-methyltransferase) activity. The enzyme or combination of enzymes responsible for this activity methylated endogenous phosphatidylethanolamine and its methylated derivatives to yield phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine. Maximum enzyme activity was expressed at pH 6.9, the reaction was not dependent on the presence of divalent cations, and exogenously added phospholipids did not stimulate the rate of reaction. Phospholipid methylation was inhibited by S-adenosyl-l-homocysteine and by local anaesthetic drugs such as chlorpromazine and tetracaine which partition into the lipid bilayer. Control experiments demonstrated that the surface membrane-associated methyltransferase activity was not due to contamination of surface membrane preparations with intracellular membranes. Surface membranes were found to have higher specific methyltransferase activities than whole L-cell homogenates or endoplasmic reticulum-enriched microsomes. The low rate of methyltransferase function expressed in vitro (approximately 1 pmol/min · mg protein) suggests that phospholipid methylation is not a major metabolic source of surface membrane phosphatidylcholine.     

The effect of dietary fat on the activity,content, rates of synthesis,and degradation and translation of messenger RNA coding for malic enzyme in mouse liver

The specific activity (units activity/mg cytosolic protein) of malic enzyme was found to be three-fold higher in the livers of mice fed a semipurified diet containing 50% ($\text{w}\text{w}$) glucose and 15% ($\text{w}\text{w}$) saturated and monounsaturated but no polyunsaturated fat (hydrogenated cottonseed oil) over an 11-day period than in the livers of mice fed a standard laboratory mouse chow (Purina) diet. In contrast, when other lab chow-fed mice were fed an isocaloric diet containing 15% ($\text{w}\text{w}$) polyunsaturated fat (corn oil), no change in the specific activity of malic enzyme occurred over a similar period of time. Rocket immunoelectrophoresis performed on cytosols from both dietary groups demonstrated that the livers of mice consuming the hydrogenated cottonseed oil diet contained approximately three times more malic enzyme protein than did the livers from the corn oil-fed animals. In mice pulse-labeled with l-[4,5-³H]leucine, the rate of hepatic malic enzyme synthesis (relative to that for total protein) was approximately twofold greater in the hydrogenated cottonseed oil-fed mice than in their corn oil-fed counterparts whereas the rate of hepatic malic enzyme degradation was similar for both groups. Immunotitration of liver malic enzyme from hydrogenated cottonseed oil-fed and corn oil-fed mice revealed identical equivalence points, demonstrating that the catalytic efficiency of mouse liver malic enzyme had not been affected by the type of dietary fat administered. When total liver RNA, isolated from the hydrogenated cottonseed oil- and the corn oil-fed animals, was translated in cell-free translation systems (wheat germ extract and reticulocyte lysate) we found that both dietary treatments had resulted in an increase in the activity of malic enzyme messenger RNA. Furthermore, there were no significant differences between the two dietary groups in this regard. These results suggest that hepatic malic enzyme specific activity in high-carbohydrate polyunsaturated fat-fed mice is regulated principally by dietary-induced changes in the rate of enzyme synthesis and not by the activity of messenger RNA coding for the enzyme.     

Complexes of vitamin B6. XVI. Kinetics and reaction mechanism of iron(III) complexes with pyridoxal-5′-phosphate

The stopped flow technique has been used to study the kinetics of complex formation of iron(III) with pyridoxal-5-phosphate (PLP) in the pH range 1.00–2.50, and in the temperature range 18 °C– 30 °C, at an ionic strength of. 0.50 M (NaCl). From the initial concentration dependence of PLP (T_PLP,) of the reaction rate it can be shown that two kinetic steps can be represented as: k_obs′ = m_i + m_i′_PLP where m_i and m_i′ are pH-dependent parameters. The calculated activation data are δE* = 23.2 ± 1.8 kcal mol^?1 and 10.98 ± 0.53 kcal mol^?1 for the first and second kinetic steps, respectively and δS* are ?20.50 ± 5.96 e.u. and 24.62 ± 1.81 e.u., respeetively.     

Mechanism of action of gastric secretory inhibitors: effects of SCN- OCN-, NO-2, and NH+4 on (H+ + K+)-ATPase-mediated transport of H+ inside gastric microsomal vesicles

The mechanisms of action of the known inhibitors of gastric acid secretion such as SCN^?, OCN^?, NO₂^?, and NH₄⁺ (M. E. LeFevre, E. J. Gohmann, Jr. and W. S. Rehm, 1964, Amer. J. Physiol.207, 613–618) were investigated using isolated pig gastric microsomal vesicles as a model system. The gastric microsomal vesicles enriched in (H⁺ + K⁺)-ATPase have previously been demonstrated to accumulate H⁺ in exchange for K⁺. The vesicular accumulation of acridine orange, which is a measure of H⁺ uptake, shows sigmoidal kinetics in the presence of increasing K⁺ with a Hill coefficient of 2.27 and a S₅₀ of 19.05 mm. None of those agents affects the microsomal (H⁺ + K⁺)-ATPase activity, although they inhibit vesicular H⁺ transport in a dose-dependent manner; the order of efficacy being NH₄⁺ > SCN^? > OCN^? > NO₂^?. The inhibitory effects of NH₄⁺ on vesicular H⁺ transport appear to be due to neutralization of the transported H⁺ by freely permeable NH₃ generated from the dissociation of NH₄⁺ in the bulk medium. SCN^?, OCN^?, and NO₂^? appear to work by a different mechanism. These agents do not act as protonophores. Our data demonstrate that the presence of SCN^?, OCN^?, and NO₂^? within the vesicle interior are essential for exerting their inhibitory effects. Furthermore, the inhibitory effects of SCN^? and OCN^? on vesicular H⁺ transport could be reversed by an elevation of intravesicular K⁺. Our data strongly suggest that the effects of SCN^?, OCN^?, and NO₂^? are exerted by interfering with a low-affinity K⁺ site (S₅₀ = 19.05 mm) within the domain of the gastric ATPase complex. This low-affinity K⁺ site is accessible only from the vesicle interior and appears to be essential for the vectorial transport of H⁺ by the gastric microsomal (H⁺ + K⁺)-ATPase system.     

Lipid/myelin basic protein multilayers. A model for the cytoplasmic space in central nervous system myelin

A multilayered complex forms when a solution of myelin basic protein is added to single-bilayer vesicles formed by sonicating myelin lipids. Vesicles and multilayers have been studied by electron microscopy, biochemical analysis, and X-ray diffraction. Freeze-fracture electron microscopy shows well-separated vesicles before myelin basic protein is added, but afterward there are aggregated, possibly multilayered, vesicles and extensive planar multilayers. The vesicles aggregate and fuse within seconds after the protein is added, and the multilayers form within minutes. No intra-bilayer particles are seen, with or without the protein. Some myelin basic protein, but no lipid, remains in the supernatant after the protein is added and the complex sedimented for X-ray diffraction. A rather variable proportion of the protein is bound. X-ray diffraction patterns show that the vesicles are stable in the absence of myelin basic protein, even under high g-forces. After the protein is added, however, lipid/myelin basic protein multilayers predominate over single-bilayer vesicles. The protein is in every space between lipid bilayers. Thus the vesicles are torn open by strong interaction with myelin basic protein. The inter-bilayer spaces in the multilayers are comparable to the cytoplasmic spaces in central nervous system myelins . The diffraction indicates the same lipid bilayer thickness in vesicles and multilayers, to within 1 A. By comparing electron-density profiles of vesicles and multilayers, most of the myelin basic protein is located in the inter-bilayer space while up to one-third may be inserted between lipid headgroups. When cytochrome c is added in place of myelin basic protein, multilayers also form. In this case the protein is located entirely outside the unchanged bilayer. Comparison of the various profiles emphasizes the close and extensive apposition of myelin basic protein to the lipid bilayer. Numerous bonds may form between myelin basic protein and lipids. Cholesterol may enhance binding by opening gaps between diacyl-lipid headgroups.     

Effects of butyric acid on cell cycle regulation and induction of histone H1(0) in mouse cells and tissue culture. Inducibility of H1 (0)in the late S-G2 phase of the cell cycle

We have examined the regulation of the synthesis of histone H1(0) in cultured mammalian cells treated with butyric acid. Treatment of cells with the inducer results in the arrest of synthesis of DNA and the other histones, while increasing the synthesis of H1(0) by a factor of 11. The induction of H1(0) by butyric acid occurs in a pulse with a peak at six hours, followed by a decrease to negligible levels. This pulse-like induction appears to be due to the fact that the cells are inducible for H1(0) only in the late S or G2 phases of the cell cycle. This, coupled with the fact that butyric acid blocks cells in G1, results in the burst of H1(0) synthesis after addition of the inducer. The G1 block provoked by butyric acid does not appear to result from the accumulation of H1(0). Removal of butyric acid from G1-blocked cells resulted in the resumption of cellular proliferation without prior loss of H1(0), demonstrating that the presence of this histone is not sufficient to prevent cellular proliferation.     

Fecundity and reproductive ecology of a natural population of Actinia equina L. (Cnidaria: Anthozoa)

Results are given of sampling Actinia populations monthly for two years, recording colour and weight of adults and weight and number of young in each adult. An anemone has a lower probability of bearing young if exposed on the rock than if one of a group in a pool, and anemones seem to migrate in and out of pools at different times of the year. In the light of these observations the hypothesis that at least some planulae leave their parent and enter another anemone is considered.