Recycling to remodel: evolution of dosage-compensation complexes

In diploid species where sex determination involves heteromorphic sex chromosomes, a mechanism has evolved to compensate for gene-dosage differences in sex-linked genes between the sexes. This regulatory mechanism, which is based on chromatin remodeling, is the function of complexes that include components themselves involved in other cellular functions or with homologs that are involved in such functions. Directing these complexes to the correct chromosome in the appropriate sex relies on pioneer or novel components as well as on the presence of sequence-dependent target sites.     

Serovar distribution of a DNA sequence involved in the antigenic relationship between Leptospira and equine cornea

Background  

Horses infected with Leptospira present several clinical disorders, one of them being recurrent uveitis. A common endpoint of equine recurrent uveitis is blindness. Serovar pomona has often been incriminated, although others have also been reported. An antigenic relationship between this bacterium and equine cornea has been described in previous studies. A leptospiral DNA fragment that encodes cross-reacting epitopes was previously cloned and expressed in Escherichia coli.     

Biocatalysis in ionic liquids: the stereoconvergent hydrolysis of trans-β-methylstyrene oxide catalyzed by soluble epoxide hydrolase

Soluble epoxide hydrolase (sEH) was shown to catalyze hydrolysis of epoxides using the ionic liquids (ILs) [bmim][PF₆], [bmim][N(Tf)₂], and [bmim][BF₄] (where bmim=1-butyl-3-methylimidazolium, PF₆=hexafluorophosphate, N(Tf)₂=bis(trifluoromethylsulfonyl)imide, and BF₄=tetrafluoroborate) as reaction medium. Reaction rates were generally comparable with those observed in buffer solution, and when the cress enzyme was used the hydrolysis of trans-β-methylstyrene oxide gave, through a stereoconvergent process, the corresponding optically active (1S,2R)-erythro-1-phenylpropane-1,2-diol.     

Choline and betaine as inducer agents of Pseudomonas aeruginosa phospholipase C activity in high phosphate medium

In Pseudomonas aeruginosa, choline or betaine employed as the sole carbon and nitrogen source in a high phosphate medium induced a phospholipase C and an acid phosphatase activity but not an alkaline phosphatase activity. The P. aeruginosa strain utilized in this work does not possess a constitutive phospholipase C, since under culture conditions identical to those utilized by other authors (J. Bacteriol. 93, 670-674 (1967) and J. Bacteriol. 150, 730-738 (1982), our phospholipase C proved to be an inorganic phosphate-repressible enzyme. These findings enable us to conclude that although the phosphate control for the synthesis of phospholipase C may exist, it is expressed only under certain favorable culture conditions.     

On the interaction of bovine pancreatic trypsin inhibitor with maxi Ca(2+)-activated K+ channels. A model system for analysis of peptide-induced subconductance states.

Bovine pancreatic trypsin inhibitor (BPTI) is a 58-residue basic peptide that is a representative member of a widely distributed class of serine protease inhibitors known as Kunitz inhibitors. BPTI is also homologous to dendrotoxin peptides from mamba snake venom that have been characterized as inhibitors of various types of voltage-dependent K+ channels. In this study we compared the effect of DTX-I, a dendrotoxin peptide, and BPTI on large conductance Ca(2+)-activated K+ channels from rat skeletal muscle using planar bilayer methodology. As previously found for DTX-I (1990. Neuron. 2:141-148), BPTI induces the appearance of distinct subconductance events when present on the internal side of maxi K(Ca) channels. The single channel kinetics of substate formation follow the predictions of reversible binding of the peptide to a single site or class of sites with a Kd of 4.6 microM at 0 mV and 50 mM symmetrical KCl. The apparent association rate of BPTI binding decreases approximately 1,000-fold per 10-fold increase in ionic strength, suggestive of a strong electrostatic interaction between the basic peptide and negative surface charge in the vicinity of the binding site. The equilibrium Kd for BPTI and DTX-I is also voltage dependent, decreasing e-fold per 30 mV of depolarization. The unitary subconductance current produced by BPTI binding exhibits strong inward rectification in the presence of symmetrical KCl, corresponding to 15% of open channel current at +60 mV and 70% of open state at -40 mV. In competition experiments, the internal pore-blocking ions, Ba2+ and TEA+, readily block the substate with the same affinity as that for blocking the normal open state. These results suggest that BPTI does not bind near the inner mouth of the channel so as to directly interfere with cation entry to the channel. Rather, the mechanism of substate production appears to involve a conformational change that affects the energetics of K+ permeation.     

Degradation of cationic surfactants using Pseudomonas putida A ATCC 12633 immobilized in calcium alginate beads

In this study, the degradation of tetradecyltrimethylammonium bromide (TTAB) by freely suspended and alginate-entrapped cells from the bacteria Pseudomonas putida (P. putida) A ATCC 12633 was investigated in batch cultures. The optimal conditions to prepare beads for achieving a higher TTAB degradation rate were investigated by changing the concentration of sodium alginate, pH, temperature, agitation rate and initial concentration of TTAB. The results show that the optimal embedding conditions of calcium alginate beads are 4 % w/v of sodium alginate content and 2 × 10⁸ cfu ml^?1 of P. putida A ATCC 12633 cells that had been previously grown in rich medium. The optimal degradation process was carried out in pH 7.4 buffered medium at 30 °C on a rotary shaker at 100 rpm. After 48 h of incubation, the free cells degraded 26 mg l^?1 of TTAB from an initial concentration of 50 mg l^?1 TTAB. When the initial TTAB concentration was increased to 100 mg l^?1, the free cells lost their degrading activity and were no longer viable. In contrast, when the cells were immobilized on alginate, they degraded 75 % of the TTAB after 24 h of incubation from an initial concentration of 330 mg l^?1 of TTAB. The immobilized cells can be stored at 4 °C for 25 days without loss of viability and can be reused without losing degrading capacity for three cycles.     

The ultrastructure of the germanium in some Rhabdocoela

Two Daphnia clones were isolated from different day depths during the period of diel vertical migration and were tested for their life-history responses to a fish exudate released by juvenile perch. Animals were exposed to fish exudate every 24 or 48 h. Both clones responded to the exudate by exhibiting earlier maturation and larger sizes of first clutches, which resulted in higher rates of population increase. Also, neonates were smaller in the presence of the exudate. It was found that the clone isolated from a deeper day depth (migrating clone) was less sensitive to the exudate than the clone isolated from the surface waters, which was presumed to be non-migrating. The non-migrating clone responded by having smaller neonate sizes and smaller sizes at maturity than the migrating clone. The non-migrating clone responded to the fish chemical when it was exposed to it every 24 or 48 h, whereas the migrating clone only responded to the exudate if exposed to it every 24 h.     

Contractile activity is required for sarcomeric assembly in phenylephrine-induced cardiac myocyte hypertrophy

Agonist-inducedhypertrophy of cultured neonatal rat ventricular myocytes (NRVM) hasbeen attributed to biochemical signals generated during receptoractivation. However, NRVM hypertrophy can also be induced byspontaneous or electrically stimulated contractile activity in theabsence of exogenous neurohormonal stimuli. Using single-cell imagingof fura 2-loaded myocytes, we found that low-density, noncontractingNRVM begin to generate intracellularCa²⁺ concentration([Ca²⁺]_i)transients and contractile activity within minutes of exposure to the₁-adrenergic agonistphenylephrine (PE; 50 µM). However, NRVM pretreated with verapamiland then stimulated with PE failed to elicit[Ca²⁺]_itransients and beating. We therefore examined whether PE-induced [Ca²⁺]_itransients and contractile activity were required to elicit specificaspects of the hypertrophic phenotype. PE treatment (48-72 h)increased cell size, total protein content, total protein-to-DNA ratio,and myosin heavy chain (MHC) isoenzyme content. PE also stimulatedsarcomeric protein assembly and prolonged MHC half-life. However,blockade of voltage-gated L-typeCa²⁺ channels with verapamil,diltiazem, or nifedipine (10 µM) blocked PE-induced total protein andMHC accumulation and prevented the time-dependent assembly ofmyofibrillar proteins into sarcomeres. Inhibition of actin-myosincross-bridge cycling with 2,3-butanedione monoxime (7.5 mM) alsoprevented PE-induced total protein and MHC accumulation, indicatingthat mechanical activity, rather than[Ca²⁺]_itransients per se, was required. In contrast, blockade of[Ca²⁺]_itransients and contractile activity did not prevent the PE-induced increase in cell surface area, activation of the mitogen-activated protein kinases ERK1 and ERK2, or upregulation of atrial natriuretic factor gene expression. Thus contractile activity is required to elicitsome but not all aspects of the the hypertrophic phenotype induced by₁-adrenergic receptoractivation.